ELECTRIC POWER SUPPLY OF GAS-DISTRIBUTING STATIONS WITH

APPLICATION OF TURBINE EXPANDER GENERATING SETS

Presenting author: I.V. Belousenko (JSC Gazprom), Co-authors: A. Yu. Zorya (JSC Gazprom promgaz), N.V.Daki (JSC Gazprom promgaz)

An important aspect of implementing gas-supply and distribution projects in remote Russian regions

relates to addressing the issues of reducing time and costs of gas pipelines and gas-distributing stations

(GDS) construction, the issues as directly influence reliability of consumer electric power supply by GDS.

Traditional GDS electric supply systems are based on external supply from the power grid and provide

for construction of a high-voltage transmission lines with a voltage rating of 6-10 kV and step-down trans-

former substations of 6-10/0.4-kV. Given the insufficient development of the power grid in the remote Rus-

sian regions, the typical length of 6-10-kV overhead transmission lines for GDS supply ranges from 5 to 10

km which, on the one hand, increases GDS-related capital investment outlay and, on the other hand, makes

consumer gas supply dependent on reliable operation of such overhead transmission lines.

While overall electric power needed for supplying a GDS is modest and varies from 2.5 to 10 kilowatt,

some of its low-energy electrical receivers are very important for the system's operation and require an inter-

ruptible supply of power. These include automatic control systems, emergency ventilation for explosion-

hazardous premises, communication and telemetric equipment, security alarms, and devices for controlling

gas consumption at the GDS. For 85-90% of all GDS under design or construction, electric load is in the

range of 2.5-5 kilowatt and has little relation to the stations' design capacity.

Reliable power supply is successfully ensured when a GDS is equipped with two independent energy

sources:

−−−− The main source of power supply: a turbine expander generating set (TEGS) of required capacity (1 or two TEGS connected in parallel and operating in an automatic standby mode);

−−−− Emergency power supply: an uninterruptible power-supply unit (UPS) equipped with a battery of re-quired capacity, ensuring uninterruptible supply to critical electrical receivers only in the event of the main power supply failure.

Choosing not to use external electric supply systems requiring the construction of 6-10 kV transmis-

sion lines makes possible an autonomous GDS operation in harsh climatic conditions adversely affecting

reliability of consumer gas supply and high-voltage lines operation. This power supply option may be used

both for construction of new facilities and for reconstruction of existing installations.

A block device for uninterrupted power supply (BDUPS) (Fig. 1,2) was especially designed as the

main or standby source of electric power for medium-capacity GDS (with an output in excess of 10000

m3/hour). Jointly designed by such Russian-based companies as JSC Gazprom promgaz, JSC Gazos-

nabzheniye, the BDUPS has a packaged-plant arrangement and contains 2 modules: the turbine expander

generating set module and the power module. The TEGS module (Fig. 3) is installed in the reducing gas-line

premises of the GDS, rated as an explosion-hazardous area. The power module is located in a heated plant

room which presents no explosion hazard.

2

Reduction Gas Line with TEGS: Flow Scheme

to the atmosphere

gas outletgas from filters

gas inlet

electricity block

Fig. 1 BDUPS of GDS

Fig. 2 BDUPS of GDS

Fig. 3 TEGS location at the GDS

The turbine expander generating set module comprises a TEGS and gas-piping accessories which

together make up one of the GDS reducing gas-lines, connected in parallel with the other reducing gas-lines

(Fig. 4).

Fig. 4 Reduction Gas Line with TEGS: Flow Scheme

Major Technical Features

1.Rated electric and technical parameters of TEGScapacity of 5kW frequency of 50 Hz voltage of 230 V

2.GDS inlet gas pressure1,2-5 MPa

3.Gas flow via TEGS200m3/h

4.TEGS pressure variation0,2 MPa

5.TEGS design: explosion-proof (GOST 22782.3-77, explosion protection 1Exsd11Т3Х), protected against adversities (IP68)

6.Parameters of the electrical and technical module:• Number of connections to commutation devices 20• Availability of automatic transfer circuit-breaker

(ATCB) function at the inlet side of 380/200 V grid with TEGS

• Availability of ATCB function between two TEGSs(optional)

• Overall dimensions of the electrical and technical module 1500х720х443 mm

• Mass of 85 kg 7. TEGS is mounted in the same premises with reduction gas lines and connected in parallel to the major reduction gas linesof the GDS

TEGS Location at the GDS

automation control room reduction control room

3

Structurally, the TEGS includes axial-type turbine expander engine (an impulse single-stage axial

turbine) put to rotation by expansion of gas flow at the turbine blades, and a brushlessly excited synchro-

nous generator with shaft elastically coupled to the turbine expander's engine shaft (Fig. 5). The generator

and turbine expander's rotors have a rotation speed of 3000 rpm. Both the turbine expander and the genera-

tor are installed inside a single cylindrical metal casing equipped with an inlet flange for connecting high-

pressure gas supply and an outlet flange for feeding gas to the low-pressure pipeline. A sealed junction-box,

used for hooking up the generator leads and connector cable, is mounted on the outside surface of the

TEGS casing. The junction-box and the TEGS casing are explosion-proof as per the Russian and interna-

tional standard GOST R 51330.1-99 (IEC 60079-1-98).

Fig. 5 Turbine Expander Generating Set

Natural gas, passing through the TEGS after being expanded in the blading section, becomes a cool-

ing medium for the generator. Gas-piping accessories comprise an electrically-driven inlet ball valve, a gas-

pressure regulator, and an manually-driven outlet ball valve. Along the gas path, the TEGS module is con-

nected in the following sequence: the GDS high-pressure header, the electrically-driven inlet ball valve, the

gas-pressure regulator, the TEGS, the manually-driven outlet ball valve, and the GDS low-pressure header.

The TEGS module is designed for operating at a maximum inlet header pressure of 5.5 millipascal. The ba-

sic TEGS parameters are: an inlet pressure of 5.5-1,2 millipascal; an outlet pressure corresponding to that in

the GDS low-pressure header; a pressure differential of 0.15 millipascal; a rated gas flow of 2000 m3/hour; a

rated electric power (at generator leads) of 5 kilowatt; a rated voltage of 230 V ± 5.5%; and a rated current

frequency of 50 Hz ± 3 Hz.

The power module (Fig. 6) is designed as a metal cabinet containing the following power equipment: a

distribution board with switching devices used for electric power input and distribution, back-up power auto-

matic enablers, a UPS, and a TEGS automatic control unit. The TEGS module is connected to the power

module with a cable line.

Turbine Expander Generating Set

1 – gas expander shell, 2 – nozzle set, 3 – turbine runner, 4 – bearing block, 5

– turbine shaft, 6 – socket, 7 – generator shell, 8 – diode box, 9 – generator

shell cover, 10- one-phase synchronous power generator with flange mounting and excitation condenser of 5 kW capacity (voltage of 230 V, rotation velocity

of 3000 rpm)

4

Fig. 6 Electrical and Technical Module

The TEGS automatic control unit maintains a permanent rotation velocity of 3000 rpm with a 6% toler-

ance, using the resistance breaking method for slowing down the generator rotor. To achieve that, the gen-

erator's active power has to be automatically maintained at a nominal value of 5 kilowatt, which corresponds

to the permanent braking-moment value at the turbine expander shaft. A special dynamic active load (active

resistance), connected via a thyristor to the generator leads, ensures a permanent value of active load for

the generator by a pulse regulation method irrespectively of GDS power consumer demand. The resistance

breaking of the rotor operation ensures stability of the electric energy's quality parameters (voltage and fre-

quency), provided the gas pressure regulator is capable of maintaining constant gas parameters through the

TEGS (a pressure differential of 0.15 millipascal at a flow of 2000 m3/hour), initially set by the operator. In

fact, resistance breaking of the generator also performs the functions of an automatic safety device prevent-

ing undue increase of the TEGS rotor rotation frequency in case of failed power supply to all GDS power

consumers. In the event of a generator damage, caused by the loss of voltage at the generator leads, the

TEGS automatic control unit shuts the electrically-operated inlet ball valve.

The main circuit of the BDUPS (Fig. 7) ensures an output of electric power from the TEGS to all con-

sumers via switching devices as well as a warm standby for critical electrical receivers via a UPS.

Fig. 7 BDUPS: Main Circuit

BDUPS of GDS: Electrical and Technical Module

front plan view with doors open

f=50 Гц

U=230В

WhОсновной

источникпитания

Потребители

III категории

230/400 В50 Гц

АВР-РЭА

I секция

II секция

I I Iсекция

АБ= 24 В

КМ1

КМ2 (байпас)

SA1230 В

АВР-АБП

АБП

ВЗ

Потребители

I категории (особая группа)

РЭА

И

BDUPS of GDS: Function Chart

turbine expander power setmajor

supply Source

section 1

section 2

section 3

230/400 V

50 Hz

3rd category

consumers

radio and electronic devices (RED)

UPS-RED

F = 50 HzU=230 V

В3

1st (special) category consumers

~230 V

ATCB-UPS

UPS

AB

bypass

SM1

SM1

=24 V

5

Crucial conditions for supplying electric power to the GDS using turbine expander generating sets are

as follows:

−−−− A strict compliance with the industrial safety requirements for operating GDS-based TEGS;

−−−− Bearing in mind that the TEGS module is integrated into the GDS process, the functioning of the TEGS or its automatic control system should not affect the regime of gas supply to the consumers or the operation of the in-line equipment.

Prevention of gas explosion and fire safety for the TEGS module is ensured by standard gas-control

and fire-extinguishing devices used at the GDS.

To prevent any effect from the TEGS operation on the GDS gas reduction regime, gas flow through

the TEGS has to be 25-30% lower than the GDS rated capacity, taking into account all consumer gas supply

fluctuations. In fact, the reduction line equipped with TEGS functions as reduction line of constant consump-

tion and this constant consumption cannot exceed minimum GDS output under the least daily and seasonal

gas supply demand.

TEGS is automatically controlled and thus has a number of specific features, including among others

the following:

−−−− Such TEGS working medium parameters as pressure and gas consumption are not involved in the regulation processes and in the reduction mode of the GDS operation have constant values as are set at the initial start-up.

−−−− Synchronous TEGS generator has no voltage control device (excitation controller), but the genera-tor voltage and reactive power can be changed stepwise by alternating capacitance of the capaci-tor switched to the exciting coil of the generator stator.

−−−− Provided constant parameters of the TEGS working medium, voltage at the generator terminals, current frequency, and generator stator currency are interrelated and vary depending on the gen-erator effective output.

−−−− The generator effective output is in fact the only available means by physically influencing TEGS to regulate the voltage and frequencies and to prevent undue increase of the rotor rotation frequency (safety regulation function).

The TEGS has operative rotation frequency of 3000 rpm, which is determined by the generated cur-

rent frequency of 50 Hz. Consequently, under this mode, efficiency of axial-type turbines cannot attain to

maximum values of the applied working medium parameters. However, when operated with rotation fre-

quency corresponding to the maximum efficiency, the TEGS operation does not influence energy parameters

of the plant. It is the largeness of GDS gas consumption margin and the wideness of allowable pressure

differentials and parameter variations that divest efficiency factor of any marked influence. Considering that,

first, the generator is cooled by the TEGS high-density working medium in quantity exceeding by many times

that required for insulation in this thermal resistance class and, second, that GDS is proof against gas con-

sumption and pressure variations, the TEGS can operate under two/three-fold overload of capacity.

Control of TEGS via electro-dynamic braking of the generator rotor is implemented by varying either

summary active generator load resistance or summary active generator current in the dynamic load, in both

cases ensuring constant electromagnetic torque on the shaft and effective output (Fig. 8).

6

Fig. 8 TEGS Regulation

Controller with alternating generator current implemented on the base of well-reputed devices is even

more feasible. In BDUPS regulation of dynamic load is underlaid by power thyristors controllable by chang-

ing dynamic loads of the generator terminals (Fig. 9). Organized under the same principles, the safety regu-

lation of TEGS is implemented by working at the thyristor key via independent channel with switching thyris-

tors under minimum commutation angle.

Fig. 9 Control of TEGS

Necessary for normal functioning of applied TEGS automatic regulation is absent generator excitation,

failing which constant value of generator stator summary current becomes requisite. However, controlling

TEGS by keeping constant summary current of the generator stator does not allow for required precision in

voltage and reactive component regulation. At the rotation velocity of 1800 rpm (less than 30 Hz), the gen-

erator has an excitation loss zone, while electromechanical time constant of the TEGS rotating parts (rotor,

runner, turbine shaft) does not exceed 1,5-2 seconds, so, when increasing or decreasing load, stability of

TEGS automated regulation (rotor electro-dynamic braking control) is ensured due to:

−−−− Selected active dynamic load resistance and thyristor commutation angles as exclude generator at-taining excitation loss;

−−−− High response rate of the dynamic load controller (time constant not exceeding 10-20 msec);

−−−− Limiting operation range of the dynamic load operator to the effective value of 240 V of the genera-tor terminal voltage, and ensuring that on attaining this value becomes active the independent thy-ristor control channel functioning as safety regulator.

Operation of a power thyristor key with pulse control of the dynamic load is associated with distorted

sinusoid of current and generator voltage. Good cooling within the TEGS shell prevents the current and volt-

Electro-dynamic braking in

TEGS Regulation

Turbine torque

Turbine decelerating torque

Turbine shaft power

Generator electromagnetic power

0

)(ω

ωТ

О

Т

М

Т

М

ТММММ −−=

ωГГ

ММ 0=

0

2

0 )(ω

ωωω

ТТ

М

Т

M

ТТММMMN −−==

)(4

)(

0

0

2

max ТТ

М

Т

МТ

ММ

МN

−

=ω

2

0 ωГГ

NN =

)(20

0

ТТ

М

Т

М

МММ

М

−

==ω

ωω

Torque curve

Power characteristics M0; N0; ω0 – nominal values

Control of the Turbine Expander Generating Set

MPa MPa

control

unit

electric power

module

to C1 &C2

~230 V

pressure control

C2

C1

7

age sinusoid highest values noticeably influencing the generator heat mode. However, acceptable quality of

electricity for GDS individual electrical receivers requiring high quality energy supply is ensured by feeding

these receivers through frequency transformer of necessary capacity.