hydropower electricity generation, 5 generator parallel ... · pdf fileparallel that also...

© Festo Didactic 86369-00 171

When you have completed this exercise, you will know how to synchronize parallel-connected synchronous generators to an ac power system. You will be familiar with the sharing of active and reactive loads between parallel-connected synchronous generators.

The Discussion of this exercise covers the following points:

Need for operating synchronous generators in parallel and associated benefits

Setting up synchronous generators for parallel operation

Active power sharing

Reactive power sharing

Frequency controller and voltage controller

Starting up a multiple-generator system

Need for operating synchronous generators in parallel and associated benefits

It is common to connect multiple synchronous generators in parallel to supply ac power to a load. The main reason is obvious: a single synchronous generator in most cases is not sufficient to supply all the active power demanded by the load. For instance, one cannot imagine that a single synchronous generator can produce all the active power demanded by the numerous consumers in a large electric power utility network. Connecting several synchronous generators in parallel is often referred to as generator paralleling.

There are other benefits inherent to the operation of synchronous generators in parallel that also explain why this strategy is commonly used to supply ac power to large loads. These benefits are listed below.

Reliability: Paralleling synchronous generators increases the reliability of an ac power system. When only a single synchronous generator is used to supply power to a load, generator failure results in complete power loss to the load. On the other hand, when parallel generators are used to supply power to a load, failure of a single generator can usually be compensated by the other generators in the system. At the very least, the remaining generators can supply the critical load (i.e., the portion of the load required to maintain operational the critical functions of the system), which generally represents only a small fraction of the total load.

Expandability: Paralleling synchronous generators allows additional generators to be added to the system as needed, thus making it much

Generator Parallel Operation and Load Sharing (Optional)

Exercise 5

EXERCISE OBJECTIVE

DISCUSSION OUTLINE

DISCUSSION

Exercise 5 – Generator Parallel Operation and Load Sharing (Optional) Discussion

172 © Festo Didactic 86369-00

easier to increase the amount of power which the generators supply to the load.

Serviceability: Paralleling synchronous generators makes it much easier to take out the generators for maintenance or repair. When only a single synchronous generator is used to supply power to a load, the system must be shut down or a standby generator must be used when the generator needs to be taken out for maintenance or repair. On the other hand, when parallel generators are used to supply power to a load, it is possible to service each synchronous generator individually, thus ensuring that the load increase is shared by the remaining generators or, at the very least, that the remaining generators continue to supply the critical load.

Flexibility: Paralleling synchronous generators gives much more flexibility when installing the generators. This is because parallel-connected generators do not need to be grouped together and can be distributed in a facility where space is available.

Figure 65. Aerial view of the Mica dam hydropower plant in British Columbia, Canada. It has a total installed capacity of 2104 MW. More than 60% of the total electrical power in Canada is generated using hydropower.

Setting up synchronous generators for parallel operation

Generally, when connecting synchronous generators in parallel, each generator unit still requires a synchro-check relay to allow proper generator synchronization, a speed governor to ensure the generator speed (frequency) is properly regulated, and an automatic voltage regulator (AVR) to ensure the generator voltage is properly regulated. This is shown in the following equipment diagram.



Figure 66. Equipment diagram of parallel-connected synchronous generators.

Hydraulic servomotor

Speed droop

Voltage droop

Speed governor

AVR

Speedcommand

( )

Voltagecommand

( )

Adjustablevane

Waterinlet

Water outlet

Synchro-check relay

Load

Synchronous generator

Thyristor bridge

Field winding


Circuit breaker

Synchronous generator 1 AC power bus

Hydraulic servomotor

Speed droop

Voltage droop

Speed governor

AVR

Speedcommand

( )

Voltagecommand

( )

Adjustable vane

Waterinlet

Water outlet

Synchro-check relay

Thyristor bridge

Field winding


Circuit breaker



For the active power sharing between the parallel-connected synchronous generators to be balanced, i.e., for the synchronous generators in the system shown above to share the active power demanded by the load (in other words,

the kW load) equally, the speed command and speed droop of the speed

governor of each generator must be set to the same values. Similarly, for the reactive power sharing to be balanced, i.e., for the synchronous generators in the system shown above to share the reactive power demanded by the load (in

other words, the kvar load) equally, the voltage command and voltage

droop of the AVR of each generator must be set to the same values. This is explained in the following two subsections of the discussion.

Active power sharing

As mentioned in the previous subsection of the discussion, when synchronous generators are connected in parallel, the speed command and speed droop must be set to the same value on each speed governor for the active power sharing to be balanced (i.e., for the kW load to be shared equally by the synchronous generators).

For example, consider two identical synchronous generators (referred to as generator 1 and generator 2), with the speed command and speed droop respectively set to 1.00 pu and 5% on each speed governor. The generators are parallel connected without any load being applied (i.e., the kW load is equal

to 0.00 pu). This sets the speed of generator 1 and the speed of generator 2 to 1.00 pu, as shown in Figure 67.

Figure 67. Operating point of the synchronous generators when the speed command and speed droop of each speed governor are set to 1.00 pu and 5%, respectively, and the kW load is equal to 0.00 pu.

In this discussion, all power

values expressed in per

units are related to the

nominal power of a single

generator.

Gene

rato

r spee

d (

pu)

Ge

ne

rato

r fr

eq

ue

ncy (

pu

)

1.10

1.05

1.00

0.95

0.90

0.00 0.02 0.04 0.06 0.08 0.10

Operating point of gen. 1 and 2 with a kW load of 0.00 pu

( 1.00 pu, 0.00 pu)

Speed regulation characteristic of gen. 1 and 2

Speed command 1.00 pu

Speed droop 5%

Generator active power (pu)

0.85

0.01 0.03 0.05 0.07 0.09



When the active power demand from the load (i.e., the kW load) passes from 0.00 pu to 1.00 pu, both synchronous generators begin to supply active power. This causes the speed (frequency) of the generators to decrease. Since the speed command and speed droop is the same for each generator, the

speed of generator 1 decreases in the same manner as the speed of generator 2, until the total active power which the generators supply is equal to the kW load. At this point, the speed and active power of each generator are equal to 0.975 pu and 0.50 pu, respectively, as is shown in Figure 68. Furthermore, the active power sharing is balanced since generator 1 and generator 2 share the kW load equally (the amount of active power supplied by each generator is equal to 0.50 pu).

Figure 68. Operating point of the synchronous generators when the speed command and speed droop of each speed governor are set to 1.00 pu and 5%, respectively, and the kW load is equal to 1.00 pu.

In the above example, if the speed command were not set to the same value on the speed governor of generator 1 and generator 2, the generators would not share the kW load equally, even if the speed droop is set to the same value on each speed governor. This is illustrated in Figure 69, which shows what happens when the speed command of generator 1 is set to 1.01 pu and the speed command of generator 2 is set to 0.99 pu. As can be seen, when the kW load is equal to 1.00 pu, both generators still rotate at a speed of 0.975 pu, but the amount of active power supplied by generator 1 is equal to 0.70 pu while the amount of active power supplied by generator 2 is equal to 0.30 pu.

Operating point of gen. 1 and 2 with a kW load of 1.00 pu

( 0.975 pu, 0.50 pu)

Speed regulation characteristic of gen. 1 and 2


Speed droop 5%

Gene

rato

r spee

d (

pu)

Ge

ne

rato

r fr

eq

ue

ncy (

pu

)

1.10

1.05

1.00

0.95

0.90

0.00 0.02 0.04 0.06 0.08 0.10


0.85

0.01 0.03 0.05 0.07 0.09



Figure 69. Operating point of the synchronous generators whose speed governors have the same speed droop (5%) but different speed commands, and the kW load is equal to 1.00 pu.

On the other hand (as shown in the above example), if the speed droop were not set to the same value on the speed governor of generator 1 and generator 2, the generators would not share the kW load equally, even if the speed command is set to the same value on each speed governor. This is illustrated in Figure 70, which shows what happens when the speed droop of generator 1 is set to 5% and the speed droop of generator 2 is set to 10%. As can be seen, when the kW load is equal to 1.00 pu, both generators rotate at a speed of 0.967 pu, but the amount of active power supplied by generator 1 is equal to 0.67 pu while the amount of active power supplied by generator 2 is equal to 0.33 pu. Note that, in the industry, it is common to set the speed droop of each speed governor in multiple generator systems to 5%.

Operating point of gen. 1 with a kW load of 1.00 pu

( 0.975 pu, 0.70 pu)

Speed regulation characteristic of gen. 1


Speed droop 5%


( 0.975 pu, 0.30 pu)



Speed droop 5%

Gene

rato

r spee

d (

pu)

Ge

ne

rato

r fr

eq

ue

ncy (

pu

)

1.10

1.05

1.00

0.95

0.90

0.00 0.02 0.04 0.06 0.08 0.10


0.85

0.01 0.03 0.05 0.07 0.09



Figure 70. Operating point of the synchronous generators whose speed governors have the same speed command (1.00 pu) but different speed droop values, and the kW load is equal to 1.00 pu.

Reactive power sharing

As mentioned in the previous subsection of the discussion, when synchronous generators are connected in parallel, the voltage command and voltage droop must be set to the same value on each AVR for the reactive power sharing to be balanced (i.e., for the kvar load to be shared equally by the synchronous generators).

For example, consider two identical synchronous generators (referred to as generator 1 and generator 2), with the voltage command and voltage droop respectively set to 1.00 pu and 5% on each AVR. The generators are parallel connected without any load being applied (i.e., the kvar load is equal to 0.00 pu).

This sets the voltage of generator 1 and the voltage of generator 2 to 1.00 pu, as shown in Figure 71.


( 0.967 pu, 0.67 pu)



Speed droop 5%


( 0.967 pu, 0.33 pu)



Speed droop 10%

Gene

rato

r spee

d (

pu)

Ge

ne

rato

r fr

eq

ue

ncy (

pu

)

1.10

1.05

1.00

0.95

0.90

0.00 0.02 0.04 0.06 0.08 0.10


0.85

0.01 0.03 0.05 0.07 0.09



Figure 71. Operating point of the synchronous generators when the voltage command and voltage droop of each AVR are set to 1.00 pu and 5%, respectively, and the kvar load is equal to 0.00 pu.

When the reactive power demand from the load (i.e., the kvar load) passes from 0.00 pu to 1.00 pu, both synchronous generators begin to supply reactive power. This causes the voltage of the generators to decrease. Since the voltage

command and voltage droop is the same for each generator, the voltage of generator 1 decreases in the same manner as the voltage of generator 2, until the total reactive power which the generators supply is equal to the kvar load. At this point, the voltage and reactive power of each generator are equal to 0.975 pu and 0.50 pu, respectively, as is shown in Figure 72. Furthermore, the reactive power sharing is balanced since generator 1 and generator 2 share the kvar load equally (the amount of reactive power supplied by each generator is equal to 0.50 pu).

Operating point of gen. 1 and 2 with a kvar load of 0.00 pu

( 1.00 pu, 0.00 pu)

Voltage regulation characteristic of gen. 1 and 2

Voltage command 1.00 pu

Voltage droop 5%

Gene

rato

r voltag

e (

pu)

1.10

1.05

1.00

0.95

0.90

0.00 0.02 0.04 0.06 0.08 0.10

Generator reactive power (pu)

0.85

0.01 0.03 0.05 0.07 0.09



Figure 72. Operating point of the synchronous generators when the voltage command and voltage droop of each AVR are set to 1.00 pu and 5%, respectively, and the kvar load is equal to 1.00 pu.

In the above example, if the voltage command were not set to the same value on the AVR of generator 1 and generator 2, the generators would not share the kvar load equally, even if the voltage droop is set to the same value on each AVR. This is illustrated in Figure 73, which shows what happens when the voltage command of generator 1 is set to 1.01 pu and the voltage command of generator 2 is set to 0.99 pu. As can be seen, when the kvar load is equal to 1.00 pu, the voltage of both generators is still equal to 0.975 pu, but the amount of reactive power supplied by generator 1 is equal to 0.70 pu while the amount of reactive power supplied by generator 2 is equal to 0.30 pu.

Operating point of gen. 1 and 2 with a kvar load of 1.00 pu

( 0.975 pu, 0.50 pu)

Voltage regulation characteristic of gen. 1 and 2


Voltage droop 5%

Gene

rato

r voltag

e (

pu)

1.10

1.05

1.00

0.95

0.90

0.00 0.02 0.04 0.06 0.08 0.10


0.85

0.01 0.03 0.05 0.07 0.09



Figure 73. Operating point of the synchronous generators whose AVRs have the same voltage droop (5%) but different voltage commands, when the kvar load is equal to 1.00 pu.

On the other hand (as shown in the above example), if the voltage droop were not set to the same value on the AVR of generator 1 and generator 2, the generators would not share the kvar load equally, even if the voltage command is set to the same value on each AVR. This is illustrated in Figure 74, which shows what happens when the voltage droop of generator 1 is set to 5% and the voltage droop of generator 2 is set to 10%. As can be seen, when the kvar load is equal to 1.00 pu, the voltage of both generators is still equal to 0.967 pu, but the amount of reactive power supplied by generator 1 is equal to 0.67 pu while the amount of reactive power supplied by generator 2 is equal to 0.33 pu. Note that, in the industry, it is common to set the voltage droop of each AVR in multiple generator systems to 5%.

Operating point of gen. 1 with a kvar load of 1.00 pu

( 0.975 pu, 0.70 pu)

Voltage regulation characteristic of gen. 1


Voltage droop 5%


( 0.975 pu, 0.30 pu)



Voltage droop 5% Gene

rato

r voltag

e (

pu)

1.10

1.05

1.00

0.95

0.90

0.00 0.02 0.04 0.06 0.08 0.10


0.85

0.01 0.03 0.05 0.07 0.09



Figure 74. Operating point of the synchronous generators whose AVRs have the same voltage command (1.00 pu) but different voltage droop values, when the kvar load is equal to 1.00 pu.

Frequency controller and voltage controller

As discussed previously in this discussion, when synchronous generators are connected in parallel to supply power to a load, the active power sharing is balanced when the speed command and speed droop are set to the same value on the speed governor of each generator. This is true no matter what the active power demand is (as long as the active power demand does not cause the generator power rating to be exceeded). However, the speed (frequency) of the generators decreases gradually as the kW load increases due to the speed droop. For instance, when the speed command and speed droop are set to 1.00 pu and 5%, respectively, the speed (frequency) of the generators passes from 1.00 pu to 0.975 pu when the increase in the kW load makes the active power supplied by each generator pass from 0.00 pu to 0.50 pu. This is shown in Figure 75.


( 0.967 pu, 0.67 pu)



Voltage droop 5%


( 0.967 pu, 0.33 pu)



Voltage droop 10%

Gene

rato

r voltag

e (

pu)

1.10

1.05

1.00

0.95

0.90

0.00 0.02 0.04 0.06 0.08 0.10


0.85

0.01 0.03 0.05 0.07 0.09



Figure 75. The speed (frequency ) of the synchronous generators decreases as the

amount of active power which they supply to the load increases.

In order to prevent the speed (frequency) of the generators from decreasing as the kW load increases, a frequency controller can be used when operating synchronous generators in parallel. The frequency controller monitors the frequency of the generators and automatically adjusts the speed command of the speed governors of the generators so as to maintain the speed (frequency) of the generators at the nominal value (i.e., 1.00 pu). For instance, increasing the speed command from 1.00 pu to 1.025 pu when the active power supplied by each generator passes from 0.00 pu to 0.50 pu as in the previous example maintains the speed (frequency) of the generators to 1.00 pu. This is illustrated in Figure 76.

Operating point of the generators after an increase of the kW load

( 0.975 pu, 0.50 pu)

Speed regulation characteristic of the generators


Speed droop 5%

Initial operating point of the generators

( 1.00 pu, 0.00 pu)

Gene

rato

r spee

d (

pu)

Ge

ne

rato

r fr

eq

ue

ncy (

pu

)

1.05

1.025

1.00

0.975

0.95

0.00 0.02 0.04 0.06 0.08 0.10


0.925

0.01 0.03 0.05 0.07 0.09



Figure 76. The speed (frequency ) of the synchronous generators is maintained

constant as the amount of active power which they supply to the load increases by increasing the speed command of the generators.

As discussed previously, when synchronous generators are connected in parallel to supply power to a load, the reactive power sharing is balanced when the voltage command and voltage droop are set to the same value on the AVR of each generator. This is true no matter what the reactive power demand is (as long as the reactive power demand does not cause the generator power rating to be exceeded). However, the voltage of the generators decreases gradually as the kvar load increases due to the voltage droop.

In order to prevent the voltage of the generators from decreasing as the kvar load increases, a voltage controller can be used when operating synchronous generators in parallel. The voltage controller monitors the voltage of the generators and automatically adjusts the voltage command of the AVRs of the generators so as to maintain the voltage of the generators at the nominal value (i.e., 1.00 pu).

Operating point of the generators after speed command increase

( 1.00 pu, 0.50 pu)

Initial speed regulation characteristic of the generators


Speed droop 5%

Speed command increase (1.00 pu to 1.025 pu)

Speed regulation characteristic of the generators after Speed command increase


Speed droop 5%

Initial operating point of the generators

( 1.00 pu, 0.00 pu)

Gene

rato

r spee

d (

pu)

Ge

ne

rato

r fr

eq

ue

ncy (

pu

)

0.00 0.02 0.04 0.06 0.08 0.10


0.01 0.03 0.05 0.07 0.09

1.05

1.025

1.00

0.975

0.95

0.925



Figure 77. Located near the city of Oroville, California, the Oroville Dam is among the tallest dams in the USA, with a height of 230 meters (770 feet). The total installed capacity of the dam is 819 MW.

Starting up a multiple-generator system

There are many different procedures for properly paralleling two or more synchronous generators. The use of one procedure over another mainly depends on the requirements of the system to which the synchronous generators are to be connected. The following steps describe a generic procedure that is commonly used in the industry. The speed command, speed droop, voltage command, and voltage droop values are also typical values.

1. The speed governor and AVR of a first synchronous generator are set as follows: speed command 1.00 pu, speed droop 5%, voltage

command 1.00 pu, voltage droop 5%.

2. Since the load is not powered yet, the synchro-check relay of the first synchronous generator is set to allow generator connection to a dead bus. Also, to avoid the power rating of the generator to be exceeded at generator connection, the load is disconnected from the power bus. Disconnecting the load from a power bus is commonly referred to as load shedding.



3. The first generator is started. When all conditions for connecting the synchronous generator to a dead bus are met, the synchro-check relay allows connection of the generator to the bus.

4. At this step, parts of the load can be reconnected to the ac power bus. The kW load applied to the first generator causes the generator speed (frequency) to decrease. The speed command of the speed governor of the generator is increased until the generator speed (frequency) is back to the nominal value (i.e., 1.00 pu). Also, in case the kvar load applied to the first generator causes the generator voltage to decrease, the voltage command of the AVR of the generator is increased until the generator voltage is back to the nominal value (i.e., 1.00 pu).

5. The speed governor and AVR of an extra synchronous generator are set as follows: speed command 1.00 pu, speed droop 5%, voltage

command 1.00 pu, voltage droop 5%.

6. Since power is now supplied to the load, the synchro-check relay of the extra synchronous generator is set to allow generator synchronization to a live bus.

7. The extra generator is started. When all conditions for synchronizing the synchronous generator to a live bus are met, the synchro-check relay allows connection of the generator to the load (i.e., the live bus). Since the speed (frequency) of the extra generator corresponds to the frequency of the live bus (i.e., 1.00 pu), the extra generator does not pick up any share of the kW load. Similarly, since the voltage of the extra generator is equal to the voltage of the live bus (i.e., 1.00 pu), the extra generator does not pick up any share of the kvar load (if any).

8. The speed command on the speed governor of each parallel-connected generator is readjusted so as to balance the active power sharing (i.e., so that the generators share the kW load equally) while maintaining the generator speed (frequency) at the nominal value (i.e., at 1.00 pu). Once the active power sharing is balanced, the speed command has the same value on the speed governor of each generator. If necessary, the voltage command on the AVR of each parallel-connected generator is readjusted so as to balance the reactive power sharing (i.e., so that the generators share the kvar load equally) while maintaining the generator voltage at the nominal value (i.e., at 1.00 pu). Once the reactive power sharing is balanced, the voltage command has the same value on the AVR of each generator.

9. Parts of the load that have been previously shed are reconnected to the ac power bus. The extra kW load applied to the parallel-connected generators causes the generator speed (frequency) to decrease. The speed command of the speed governor of each generator is increased in the same manner (to preserve balanced active power sharing) until the generator speed (frequency) is back to the nominal value (i.e., 1.00 pu). Also, in case the extra kvar load applied to the parallel-connected generators causes the generator voltage to decrease, the voltage command of the AVR of each generator is increased in the same manner (to preserve balanced reactive power sharing) until the generator voltage is back to the nominal value (i.e., 1.00 pu).

Exercise 5 – Generator Parallel Operation and Load Sharing (Optional) Procedure Outline


10. Steps 5 to 8 are repeated whenever an extra synchronous generator is connected in parallel with the other generators. Step 9 is repeated whenever parts of the load that have been previously shed are reconnected to the ac power bus.

In the above procedure, both the kW load and the kvar load are shared equally between the parallel-connected generators. Other strategies can be used to share the kW load and kvar load among the generators. The study of these strategies, however, is beyond the scope of this manual.

Figure 78. Aerial view of the Inga I dam hydropower plant located on the Congo River in Congo. Projects are underway to harness the mostly unused hydroelectrical potential of the large Congo River (photo courtesy of Alaindg).

The Procedure is divided into the following sections:

Set up and connections

Active power sharing (kW load sharing) between generators connected to the same bus

Reactive power sharing (kvar load sharing) between generators connected to the same bus

High voltages are present in this laboratory exercise. Do not make or modify any

banana jack connections with the power on unless otherwise specified.

PROCEDURE OUTLINE

PROCEDURE

Exercise 5 – Generator Parallel Operation and Load Sharing (Optional) Procedure


Set up and connections

a This exercise is optional because two student groups must collaborate (i.e., put equipment from two training systems together) to perform it. Also, note that the procedure is performed using the SCADA view of the Synchronous Generator Control window. It is therefore recommended to read Appendix E as an introduction to SCADA systems before performing the following manipulations.

In this section, you will set up two synchronous generators, each driven by a hydraulic turbine and connected to a three-phase resistive-inductive load through a three-phase contactor. You will then set up the measuring equipment required to study the parallel operation of the generators.

1. Refer to the Equipment Utilization Chart in Appendix A to obtain the list of equipment required to perform this exercise.

Install the required equipment in the workstations. It is recommended to install all equipment from one system into the one Workstation, and all equipment from the other system into the other Workstation. Throughout the exercise, all equipment installed in or pertaining to the first workstation is referred to as system 1, while all equipment installed in or pertaining to the second workstation is referred to as system 2.

a Although the Equipment Utilization Chart indicates that only one Power Supply is necessary to perform this exercise, it is recommended to use two Power Supply modules if possible (one for each system). This ensures that both systems are completely independent from each other (except for the leads used for parallel connection of the generators).

Before coupling rotating machines, make absolutely sure that power is turned off

to prevent any machine from starting inadvertently.

In each system, mechanically couple the Synchronous Motor/Generator to the Four-Quadrant Dynamometer/Power Supply using a timing belt.

2. In each system, perform the following manipulations:

Make sure the ac and dc power switches on the Power Supply are set to the O (off) position, then connect the Power Supply to a three-phase ac power outlet.

Make sure the main power switch on the Four-Quadrant Dynamometer/Power Supply is set to the O (off) position, then connect the Power Input to an ac power outlet.

Connect the Power Input of the Data Acquisition and Control Interface to a 24 V ac power supply.

Connect the Low Power Input of the Power Thyristors module to the Power Input of the Data Acquisition and Control Interface. Turn the 24 V ac power supply on.




Connect the USB port of the Data Acquisition and Control Interface to a USB port of the host computer.

Connect the USB port of the Four-Quadrant Dynamometer/Power Supply to a USB port of the host computer.

4. In each system, turn the Four-Quadrant Dynamometer/Power Supply module on, then set the Operating Mode switch to Dynamometer.

5. In each system, turn the host computer on, then start the LVDAC-EMS software.

In the LVDAC-EMS Start-Up window of each system, make sure the Data Acquisition and Control Interface and the Four-Quadrant Dynamometer/Power Supply are detected. Make sure the Computer-Based Instrumentation and Synchronous Generator Control functions are available for the Data Acquisition and Control Interface modules. Make sure that the Turbine Emulator function is available for the Four-Quadrant Dynamometer/Power Supply. Also, select the network voltage and frequency that correspond to the voltage and frequency of the local ac power network, then click the OK button to close the LVDAC-EMS Start-Up window.

6. Connect the equipment as shown in Figure 79. Use a Four-Quadrant Dynamometer/Power Supply to implement each hydraulic-turbine emulator. Use the Power Supply to implement the two three-phase ac power sources (or, if you use two Power Supply modules, use each one of them to implement a three-phase ac power source). Use a Power Thyristors module to implement each thyristor three-phase bridge. Finally, in each system, use

a Resistive Load to implement resistors , , and , and use an Inductive Load to implement inductors , , and .

When connecting each thyristor three-phase bridge, make sure switches S1 and S2 on the Power Thyristors module are set to the I (closed) position. Doing so connects thyristors Q1 to Q6 in a three-phase bridge configuration.

a In the circuit of Figure 79, inputs E2, E3, E4, I3, and I4 in system 1 are used to measure the circuit parameters necessary for controlling the synchronous generator when it is connected to a dead bus. Also, inputs E2, E3, E4, I3, and I4 in system 2 are used to measure the circuit parameters necessary for controlling the synchronous generator when it is connected to a live bus powered by one or more synchronous generators (generator paralleling). Because of this, inputs E2, E3, E4, I3, and I4 in both systems cannot be used for circuit parameter measurement and observation in this exercise.



The equipment setup shown in Figure 79 represents two synchronous generators in a hydropower plant supplying power to electrical power consumers (represented by the three-phase resistive-inductive load). When the two synchronous generators are connected together and operate simultaneously, they supply ac power to the network (i.e., the resistive-inductive load). Note that, although the emulated hydropower plant contains only two synchronous generators, the principles of operation are the same for a hydropower plant of any size (i.e., containing multiple synchronous generators connected in parallel).



Figure 79. Two parallel-connected turbine-driven (hydropower) synchronous generators, each connected to a three-phase resistive-inductive load (ac power bus) through a three-phase contactor.


Hydraulic-turbine

emulator

L1

L2

L3

Three-phase contactor

Thyristor three-phase bridge

L1

L2

L3

N

Resistive-inductive

load


Hydraulic-turbine

emulator

L1

L2

L3

Three-phase contactor

Control signal from DACI

Thyristor three-phase bridge

L1

L2

L3

N

Equipment setup in 1st

workstation (system 1)

Equipment setup in 2nd

workstation (system 2)

To neutral terminal of both synchronous generators

To neutral terminal of both synchronous generators

Control signal from DACI

Firing signals from DACI

Firing signals from DACI



7. In the first system, make the required setting to obtain the combination of resistance and reactance values indicated in Table 20. This combination of resistance and reactance values provides a minimal load ensuring proper system operation.

Table 20. Resistance values of , , and , and reactance values of , , and to be used in the circuit of Figure 79.

Local ac power network Resistance values of , ,

and , and reactance values of , , and Voltage

(V)

Frequency

(Hz)

120 60 1200

220 50 4400

240 50 4800

220 60 4400

8. In each system, make sure the Sync. switch on the Synchronizing Module/Three-Phase Contactor is set to the O position. This allows remote control of the three-phase contactor by the Data Acquisition and Control Interface module.

9. In each system, connect the Digital Outputs of the Data Acquisition and Control Interface to the Firing Control Inputs of the Power Thyristors module using the provided cable with DB9 connectors.


Connect Digital Output 1 (DO1) of the Data Acquisition and Control Interface to the positive (+) terminal of the Remote Control input on the Synchronizing Module/Three-Phase Contactor using a miniature banana plug lead. Connect a digital (D) common (white terminal) of the Data Acquisition and Control Interface to the negative (-) terminal of the Remote Control input on the Synchronizing Module/Three-Phase Contactor using a miniature banana plug lead.

Connect Analog Output 1 (AO1) of the Data Acquisition and Control Interface to the left-hand side terminal of the Command Input of the Four-Quadrant Dynamometer/Power Supply using a miniature banana plug lead. Connect an analog (A) common (white terminal) on the Data Acquisition and Control Interface to the common (white terminal) of the Command Input on the Four-Quadrant Dynamometer/Power Supply using a miniature banana plug lead.



Connect the A Shaft Encoder Output of the Four-Quadrant Dynamometer/Power Supply to the A Encoder Digital Input of the Data Acquisition and Control Interface using a miniature banana plug lead. Connect the B Shaft Encoder Output of the Four-Quadrant Dynamometer/Power Supply to the B Encoder Digital Input of the Data Acquisition and Control Interface using a miniature banana plug lead. Connect the common (white terminal) of the Shaft Encoder Outputs on the Four-Quadrant Dynamometer/Power Supply to a digital (D) common (white terminal) of the Encoder Digital Inputs on the Data Acquisition and Control Interface using a miniature banana plug lead.

11. On each Synchronous Motor/Generator, set the Exciter switch to the closed position (I), then turn the Exciter knob fully clockwise (i.e., set it to the Max. position).

Active power sharing (kW load sharing) between generators connected to the same bus

In this section, you will connect the first synchronous generator to the three-phase resistive-inductive load, then adjust the generator speed and voltage commands so that the generator frequency and voltage are equal to the nominal values. You will then synchronize the second synchronous generator to the first synchronous generator. You will adjust the speed command of each generator so that the kW load in the system is shared equally. You will successively increase and decrease the active power demand (i.e., the kW load applied to the system) and observe the effects on the speed, frequency, and active power of each synchronous generator. While doing so, you will readjust the speed command of the speed governor of each synchronous generator so as to bring the generator speed and frequency back to the nominal value (while keeping the active power sharing balanced). You will analyze the results.

12. In LVDAC-EMS (system 1), open the Synchronous Generator Control window. In this window, click on the Show SCADA View button to switch to a SCADA view of the Synchronous Generator Control window. The SCADA view of the Synchronous Generator Control window allows all important

parameters (e.g., generator voltage , frequency , active power , hydraulic-turbine vane opening, speed , torque , and mechanical

power at the generator shaft, etc.) measured during operation of the hydropower generator to be visualized in a single window. It also allows the settings of the hydropower generator and hydraulic-turbine emulator to be adjusted from a single window.

In the Synchronous Generator Control window of system 1, temporarily display the Four-Quadrant Dynamometer/Power Supply Settings window to make the following settings:

Make sure the Turbine Type parameter is set to 300 W, Francis.

Make sure the Vane Maximal Speed parameter is set to 10.0%/s.

Make sure the Runner Inertia parameter is set to 0.3 kg·m2.



Make sure the Hydraulic-Turbine Emulator function is set to Stopped.

In the Synchronous Generator Control window of system 1, temporarily display the Hydropower Generator Control Settings window to make the following settings:

Make sure the Function parameter is set to Hydropower Generator (Dead Bus – Balanced Load).

Make sure the Nominal Voltage parameter is set to the nominal value of the local ac power network voltage.

Make sure the Hydropower Generator (Dead Bus – Balanced Load) function is set to Stopped.

Synchro-Check Relay

Make sure the Live Bus Voltage Threshold parameter is set to 90% of the ac power network nominal voltage .

Make sure the Relay Output parameter is set to Normal.

Make sure the Dead Bus Voltage Threshold parameter is set to 10% of the ac power network nominal voltage .

Make sure the Dead Time parameter is set to 1 s.

Speed Governor

Make sure the Generator Speed Command parameter is set to the nominal synchronous speed of the synchronous generator (i.e., 1.00 pu).

a The nominal synchronous speed of the Synchronous Motor/Generator is 1500 r/min at a local ac power network frequency of 50 Hz and 1800 r/min at a local ac power network frequency of 60 Hz.

Make sure the Speed Droop parameter is set to 5%.

Make sure the Generator Acceleration parameter is set to 30 r/min / s.

Make sure the Proportional Gain [Kp] is set to 20.

Make sure the Derivative Gain [Kd] is set to 40.

Automatic Voltage Regulator

Make sure the Thyristor Bridge Firing Control Mode parameter is set to Automatic.

Make sure the Generator Voltage Command parameter is set to the nominal value of the local ac power network line voltage (i.e., 1.00 pu).



Make sure the Voltage Droop parameter is set to 5%.

Make sure the Minimum Firing Angle Limit parameter is set to 40°.

Make sure the Maximum Firing Angle Limit parameter is set to 120°.

Make sure that the Proportional Gain [Kp] parameter is set to the value indicated in the following table that corresponds to your local ac power network voltage and frequency.

Table 21. Proportional gain Kp of the automatic voltage regulator of the hydropower generator.

Local ac power network Proportional gain

Kp Voltage (V)

Frequency (Hz)

120 60 5

220 50 2

240 50 1.25

220 60 2

Make sure that the Integral Gain [Ki] parameter is set to the value indicated in the following table that corresponds to your local ac power network voltage and frequency.

Table 22. Integral gain Ki of the automatic voltage regulator of the hydropower generator.

Local ac power network

Integral gain Ki Voltage

(V) Frequency

(Hz)

120 60 20

220 50 10

240 50 5

220 60 10

13. In system 1, perform the following manipulations:

On the Power Supply, turn the three-phase ac power source on.

In the Synchronous Generator Control window, start the hydraulic-turbine emulator by clicking the Start/Stop (Emulator) button.

In the Synchronous Generator Control window, start the hydropower generator by clicking the Start/Stop (Controller) button.



14. Wait a few seconds. Does the synchro-check relay in system 1 allow connection of the synchronous generator to the resistive-inductive load (i.e., to the dead bus)?

Yes No

a In the rest of this exercise, the synchronous generator in system 1 is referred to as generator 1.

15. In each system, make the necessary switch settings on the Resistive Load and the Inductive Load to obtain the 1

st combination of resistance and

reactance values indicated in Table 23.

Table 23. Resistance values of , , and , and reactance values of , , and to be used in the circuit of Figure 79.

Local ac power network Resistance values of , , and , and reactance values

of , , and

Voltage

(V)

Frequency

(Hz)

1st

( )

2nd

( )

3rd

( )

4th

( )

5th

( )

6th

( )

120 60 400 300 600 1200 1200 1200

400 600

220 50 1467 1100 2200 4400 4400 4400

1467 2200

240 50 1600 1200 2400 4800 4800 4800

1600 2400

220 60 1467 1100 2200 4400 4400 4400

1467 2200

16. Wait for the speed and voltage of generator 1 to stabilize. In the Synchronous Generator Control window of system 1, measure and record (in the spaces below) the speed , frequency , voltage , and active

power of the generator. Express the values of the measured parameters using conventional units as well as per units.

Generator speed r/min

Generator frequency Hz

Generator voltage V

Generator active power W



17. Observe that the speed (frequency ) of generator 1 is well below the speed command value (1.00 pu). Also observe that the active

power is close to 1.00 pu.

a In this exercise, all power values expressed in per units are related to the nominal power of a single generator (i.e., 200 VA).

Explain why the speed (frequency ) of generator 1 falls well below the speed command value (1.00 pu) when the generator is connected to the resistive-inductive load.

18. In the Synchronous Generator Control window of system 1, adjust the

Generator Speed Command so that the frequency of generator 1 is equal to the nominal frequency of the local ac power network.

Record (in the spaces below) the speed command value ( )

required to maintain the frequency of generator 1 at the nominal value when operating with the current load. Also record the first generator active

power . Express the values of the measured parameters using conventional units as well as in per units.

Generator speed command

Generator active power

19. In LVDAC-EMS (system 2), open the Synchronous Generator Control window. In this window, click on the Show SCADA View button to switch to a SCADA view of the Synchronous Generator Control window.

In the Synchronous Generator Control window of system 2, temporarily display the Four-Quadrant Dynamometer/Power Supply Settings window to make the following settings:

Make sure the Turbine Type parameter is set to 300 W, Francis.

Make sure the Vane Maximal Speed parameter is set to 10.0%/s.

Make sure the Runner Inertia parameter is set to 0.3 kg·m2.

Make sure the Hydraulic-Turbine Emulator function is set to Stopped.



In the Synchronous Generator Control window of system 2, temporarily display the Hydropower Generator Control Settings window to make the following settings:

Set the Function parameter to Hydropower Generator (Gen. Paralleling – Balanced Bus). This function allows control of a turbine-driven (hydropower) generator connected to a balanced generator bus (i.e., a bus consisting of one or more synchronous generators). The function includes a synchro-check relay used for synchronizing the generator to the generator bus.

Make sure the Nominal Voltage parameter is set to the nominal value of the local ac power network voltage.

Make sure the Hydropower Generator (Gen. Paralleling – Balanced Bus) function is set to Stopped.

Synchro-Check Relay

Make sure the Live Bus Voltage Threshold parameter is set to 90% of the ac power network nominal voltage .

Make sure the Voltage Difference E parameter is set to 5% of the ac power network nominal voltage.

Make sure the Frequency Difference f parameter is set to 0.2 Hz.

Make sure the Phase Difference parameter is set to 20°.

Make sure the Circuit-Breaker Operate Time parameter is set to 0.05 s.

Make sure the Relay Output parameter is set to Normal.

Speed Governor

Make sure the Generator Speed Command parameter is set to the nominal synchronous speed of the synchronous generator (i.e., 1.00 pu).

Make sure the Speed Droop parameter is set to 5%.

Make sure the Generator Acceleration parameter is set to 30 r/min / s.

Make sure the Proportional Gain [Kp] is set to 20.

Make sure the Derivative Gain [Kd] is set to 40.



Automatic Voltage Regulator

Make sure the Thyristor Bridge Firing Control Mode parameter is set to Automatic.

Make sure the Generator Voltage Command parameter is set to the nominal value of the local ac power network line voltage (i.e., 1.00 pu).

Make sure the Voltage Droop parameter is set to 5%.

Make sure the Minimum Firing Angle Limit parameter is set to 40°.

Make sure the Maximum Firing Angle Limit parameter is set to 120°.

Make sure that the Proportional Gain [Kp] parameter is set to the value indicated in the following table that corresponds to your local ac power network voltage and frequency.

Table 24. Proportional gain Kp of the automatic voltage regulator of the hydropower generator.

Local ac power network Proportional gain

Kp Voltage (V)

Frequency (Hz)

120 60 5

220 50 2

240 50 1.25

220 60 1.5

Make sure that the Integral Gain [Ki] parameter is set to the value indicated in the following table that corresponds to your local ac power network voltage and frequency.

Table 25. Integral gain Ki of the automatic voltage regulator of the hydropower generator.

Local ac power network

Integral gain Ki Voltage

(V) Frequency

(Hz)

120 60 20

220 50 10

240 50 5

220 60 8


On the Power Supply, turn the three-phase ac power source on (only if two Power Supply modules are used).



In the Synchronous Generator Control window, start the hydraulic-turbine emulator by clicking the Start/Stop (Emulator) button.

In the Synchronous Generator Control window, start the hydropower generator by clicking the Start/Stop (Controller) button.

21. Wait a few seconds. Does the synchro-check relay in system 2 allow connection of the second synchronous generator to generator 1 (i.e., the generator bus)?

Yes No

a In the rest of this exercise, the synchronous generator in system 2 is referred to as generator 2.

22. Wait for the amount of active power supplied to the load by each synchronous generator to stabilize. Then, measure and record (in the spaces below) the speed command, speed, frequency, and active power of each synchronous generator. Express the values of the measured parameters using conventional units as well as per units.

Generator 1

Speed command

Speed

Frequency

Active power

Generator 2

Speed command

Speed

Frequency

Active power



What do the active power values you just recorded indicate about the active power sharing (i.e., the kW load sharing) between the two synchronous generators? Explain briefly.

23. In the Synchronous Generator Control window of system 1, decrease the Generator Speed Command parameter by 0.017 pu.

In the Synchronous Generator Control window of system 2, increase the Generator Speed Command parameter by 0.017 pu.


Generator 1

Speed command

Speed

Frequency

Active power

Generator 2

Speed command

Speed

Frequency

Active power



Is the sum of the active power values you just recorded virtually equal to the sum of the active power values you recorded in step 22, indicating that the same amount of active power is supplied to the load even though the speed commands of the generators have been modified? Explain briefly.

What do the active power values you just recorded indicate about the active power sharing (i.e., the kW load sharing) between the two synchronous generators? Explain briefly.

25. In the Synchronous Generator Control window of each system, continue to adjust the Generator Speed Command parameter until the kW load in the system is shared equally between the two synchronous generators (i.e., until each synchronous generator supplies the same amount of active power to the load).

26. Measure and record (in the spaces below) the speed command, speed, frequency, and active power of each synchronous generator. Express the values of the measured parameters using conventional units as well as per units.

Generator 1

Speed command

Speed

Frequency

Active power



Generator 2

Speed command

Speed

Frequency

Active power

Is the sum of the active power values you just recorded equal to the sum of the active power values you recorded in step 22 and step 24, indicating that the same amount of active power is supplied to the load even though the speed commands of the generators have been modified so that each generator supplies an identical amount of active power to the load?

Yes No

From the results you recorded in this step, what conditions must be met to ensure perfect active power sharing (i.e., to ensure that the parallel-connected generators share the kW load equally)?

27. Make the necessary switch settings on the Resistive Load and the Inductive Load to obtain the 2

nd combination of resistance and reactance values

indicated in Table 23. This combination of resistance and reactance values increases the active power demand (i.e., the kW load).


Generator 1

Speed command

Speed

Frequency

Active power



Generator 2

Speed command

Speed

Frequency

Active power

Considering the active power values you just recorded, can you conclude that the synchronous generators shared the increase in active power demand (i.e., the kW load increase) equally? Explain briefly.

29. Compare the speed (frequency) of the synchronous generators you recorded in the previous step to the speed (frequency) of the synchronous generators you recorded in step 26. Has the kW load increase caused the speed (frequency) of the synchronous generators to decrease? Explain briefly.

What should be done in this situation to bring the generator speed (frequency) back to the nominal value while ensuring that the active power sharing remains balanced (i.e., that the generators continue to share the load equally)?



30. In the Synchronous Generator Control window of each system, adjust the Generator Speed Command parameter the same way (i.e., change the parameter value by the same amount) until the speed (frequency) of the synchronous generators is equal to the nominal value.

Does this confirm your answer to the 2nd

question in the previous step?

Yes No


rd combination of resistance and reactance values

indicated in Table 23. This combination of resistance and reactance values decreases the active power demand (i.e., the kW load).


Generator 1

Speed command

Speed

Frequency

Active power

Generator 2

Speed command

Speed

Frequency

Active power

Considering the active power values you just recorded, can you conclude that the synchronous generators shared the decrease in active power demand (i.e., the kW load decrease) equally? Explain briefly.



33. Compare the speed (frequency) of the synchronous generators you recorded in the previous step to the speed (frequency) of the synchronous generators you obtained in step 28. Has the kW load decrease caused the speed (frequency) of the synchronous generators to increase? Explain briefly.

What should be done in this situation to bring the generator speed (frequency) back to the nominal value while ensuring that the active power sharing remains balanced (i.e., that the generators continue to share the load equally)?

34. Considering your observations, explain briefly how the frequency of parallel-connected synchronous generators can be automatically maintained at the nominal value no matter the active power demand (i.e., the kW load applied to the system).



35. In the Synchronous Generator Control SCADA View window of system 1, set the Generator Speed Command parameter to the value indicated in the following table.

Table 26. Speed command of the generator in system 1.

Local ac power network Generator speed

command (pu)

Voltage (V)

Frequency (Hz)

120 60 1.024

220 50 1.022

240 50 1.024

220 60 1.022

In the Synchronous Generator Control SCADA View window of system 2, set the Generator Speed Command parameter to the value indicated in the following table.

Table 27. Speed command of the generator in system 2.

Local ac power network Generator speed

command (pu)

Voltage (V)

Frequency (Hz)

120 60 1.012

220 50 1.011

240 50 1.012

220 60 1.011

a Note that this unbalances the active power sharing (i.e., the generators no longer share the kW load equally).


Generator 1

Speed command

Speed

Frequency

Active power



Generator 2

Speed command

Speed

Frequency

Active power


st combination of resistance and reactance values

indicated in Table 23. This combination of resistance and reactance values increases the active power demand (i.e., the kW load).


Generator 1

Speed command

Speed

Frequency

Active power

Generator 2

Speed command

Speed

Frequency

Active power



39. Compare the active power values you just recorded to those you recorded in step 36. Can you conclude that the synchronous generators shared the kW load increase equally (i.e., that the amount of active power supplied to the load by each synchronous generator increased by the same amount), even though their speed commands are not equal? Explain briefly.

Reactive power sharing (kvar load sharing) between generators connected to the same bus

In this section, you will set the resistance of the three-phase load to a low value while keeping the inductive reactance infinite. You will adjust the speed command of each generator so that the generator frequency is equal to the nominal value and the active power sharing is balanced. You will measure the parameters (speed command, speed, frequency, active power, voltage command, voltage, and reactive power) of each generator. You will successively increase and decrease the reactive power demand (i.e., the kvar load applied to the system) and observe the effects on the voltage and reactive power of each synchronous generator. While doing so, you will readjust the voltage command of the AVR of each synchronous generator so as to bring the generator voltage back to the nominal value (while keeping the reactive power sharing balanced). You will analyze the results.


th combination of resistance and reactance values

indicated in Table 23.

41. In the Synchronous Generator Control window of each system, adjust the Generator Speed Command parameter until each synchronous generator supplies the same amount of active power to the load.

In the Synchronous Generator Control window of each system, adjust the Generator Speed Command parameter the same way (i.e., change the parameter value by the same amount) until the speed (frequency) of the synchronous generators is equal to the nominal value.

42. Measure and record (in the spaces below) the speed command, speed, frequency, active power, voltage command, voltage, and reactive power of each synchronous generator. Express the values of the measured parameters using conventional units as well as per units.



Generator 1

Speed command

Speed

Frequency

Active power

Voltage command

Voltage

Reactive power

Generator 2

Speed command

Speed

Frequency

Active power

Voltage command

Voltage

Reactive power

43. In the Synchronous Generator Control window of each system, adjust the Generator Voltage Command parameter until each synchronous generator exchanges the same amount of reactive power with the load, if necessary.

a This step is often necessary to compensate the offset in the amount of reactive power exchanged by each synchronous generator. This offset, when observed, is caused by the measurement error introduced by the voltage sensor in each AVR.



indicated in Table 23. This combination of resistance and reactance values adds a reactive power demand (i.e., applies a kvar load to the generators).



45. Wait for the amount of reactive power exchanged with the load by each synchronous generator to stabilize. Then, measure and record in the spaces below) the voltage command, voltage, and reactive power of each synchronous generator. Express the values of the measured parameters using conventional units as well as per units.

Generator 1

Voltage command

Voltage

Reactive power

Generator 2

Voltage command

Voltage

Reactive power

Considering the reactive power values you just recorded, can you conclude that the synchronous generators shared the reactive power demand (i.e., the kvar load) equally? Explain briefly.

46. Compare the voltage of the synchronous generators you recorded in the previous step to that you measured in step 42. Has the reactive power demand caused the voltage of the synchronous generators to decrease? Explain briefly.



What should be done in this situation to bring the generator voltage back to the nominal value while ensuring that the reactive power sharing remains balanced (i.e., that the generator continues to share the kvar load equally)?

47. In the Synchronous Generator Control window of each system, adjust the Generator Voltage Command parameter the same way (i.e., change the parameter value by the same amount) until the voltage of the synchronous generators is equal to the nominal value.

Does this confirm your answer to the 2nd

question in the previous step?

Yes No



indicated in Table 23. This combination of resistance and reactance values decreases the reactive power demand (i.e., the kvar load).

49. Wait for the amount of reactive power exchanged with the load by each synchronous generator to stabilize. Then, measure and record (in the spaces below) the voltage command, voltage, and reactive power of each synchronous generator. Express the values of the measured parameters using conventional units as well as per units.

Generator 1

Voltage command

Voltage

Reactive power

Generator 2

Voltage command

Voltage

Reactive power



Considering the reactive power values you just recorded, can you conclude that the synchronous generators shared the decrease in reactive power demand (i.e., the kvar load decrease) equally? Explain briefly.

50. Compare the voltage of the synchronous generators you recorded in the previous step to that you obtained in step 45. Has the kvar load decrease caused the voltage of the synchronous generators to increase? Explain briefly.

What should be done in this situation to bring the generator voltage back to the nominal value while ensuring that the reactive power sharing remains balanced (i.e., that the generator continues to share the kvar load equally)?

51. Considering your observations, explain briefly how the voltage of parallel-connected synchronous generators can be automatically maintained at the nominal value no matter the reactive power demand (i.e., the kvar load applied to the system).


In the Synchronous Generator Control window, adjust the Generator Speed Command and Generator Voltage Command parameters so

that the generator active power and reactive power are virtually null.

Exercise 5 – Generator Parallel Operation and Load Sharing (Optional) Conclusion


In the Synchronous Generator Control window, set the Relay Output parameter to Low to force disconnection of the synchronous generator from the bus, then set the Generator Speed Command and Generator Voltage Command parameters to 0. Wait for the hydraulic turbine driving the generator to stop rotating, then stop the hydropower generator by clicking the Start/Stop (Controller) button.

In the Synchronous Generator Control window, stop the hydraulic-turbine emulator by clicking the Start/Stop (Emulator) button.


In the Synchronous Generator Control window, set the Relay Output parameter to Low to force disconnection of the synchronous generator from the bus, then set the Generator Speed Command and Generator Voltage Command parameters to 0. Wait for the hydraulic turbine driving the generator to stop rotating, then stop the hydropower generator by clicking the Start/Stop (Controller) button.

In the Synchronous Generator Control window, stop the hydraulic-turbine emulator by clicking the Start/Stop (Emulator) button.

On the Power Supply (or on the two Power Supply modules), turn the three-phase ac power source off.

54. Close LVDAC-EMS, then turn off all the equipment. Disconnect all leads and return them to their storage location.

In this exercise, you learned how to synchronize parallel-connected synchronous generators to an ac power system. You became familiar with the sharing of the kW load and kvar load between parallel-connected synchronous generators.

1. Consider a series of synchronous generators having the same power rating that need to be connected to an ac power system consisting of a resistive and reactive load. Briefly explain the procedure for connecting the first synchronous generator to the system.

CONCLUSION

REVIEW QUESTIONS

Exercise 5 – Generator Parallel Operation and Load Sharing (Optional) Review Questions


2. Consider that the synchronous generator described in Question 1 is connected to the ac power system and operates at nominal frequency and voltage. Briefly explain the procedure for connecting other similar synchronous generators to the system.

3. Consider an ac power system consisting of several synchronous generators with the same power rating and speed droop percentage supplying active power to a load. All synchronous generators operate at nominal frequency and share the active load equally. Briefly explain the procedure for sharing the active load when a similar synchronous generator with a speed command equal to the nominal speed is added to the system.

Exercise 5 – Generator Parallel Operation and Load Sharing (Optional) Review Questions


4. Consider an ac power system consisting of several synchronous generators with the same power rating and speed and voltage droop percentages supplying active and reactive power to a load. All synchronous generators operate at nominal frequency and voltage. Briefly explain the procedure for sharing the reactive load when a similar synchronous generator with speed and voltage commands equal to the nominal speed and voltage, respectively, is added to the system.

5. Consider two synchronous generators with the same power rating supplying power to an active load. The speed droop of both synchronous generators is 10% and their frequency is equal to the nominal value. The total amount of active power they supply to the load is equal to 0.9 pu and they operate at nominal frequency. Calculate the required speed commands of the synchronous generators so that they operate at the nominal frequency when a third similar synchronous generator is added to the system.

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