What is EOCR ?

1. Preface

Traditionally, TORs have being used for motors for a long time. But developing of the electronics

technology tends for people to apply its technology to every industrial field with its accurcy and

flexibility. According to this trends, EOCR came out to electric industry field. EOCR has three main

parts which are the sensor part detecting current, the process part caculating and deciding the

sensing value, and the output part resulted from the processing. The accuracy and flexibility of

electronics let them protect not only motors but also mechanical loads connected to the motors.

The mechanical load and the current of motor are in indispensible relation. There is one important

principle in this, That is, we can surmise the status of mechanical load and a motor from monitoring

the current of the motors. If the mechanical load increases, the current of motor also get to

increase. The abnormal increase of mechanical load tells us some problems are happening in

there and results in a burned motor and broken machine. We can diagnose and protect the motor

system by checking the current of motors with eletronic technology. Usually when we design the

machines using a motor, we set the rating of the motor higher than the one of machine in

cosideration of safety, reserve and economy. So both ratings of the motor and machnine are not

same. While we sets the current value at the rating current of motors in TOR, but we sets the

current value at the rating of machine load by using the ammeter function in EOCR. By this, we

are able to diagnose the status of the mecanical load and motors. For example , let ’s assume that

there is a pump hindered by unexpected foreign material. then the current of motor comes to

increase and means some problems are happening in there. If the current of motor does not

increase over the rating of the motor, the TOR will not be tripped. As a result, this overload of the

pump can proceed to bigger problem. But EOCR will be tripped instantly as to the actual set

current value not to proceed to bigger problem.

1

Mechanical Load

( 100 % )

Increase

Decrease

Current ofMotor

( 80% or so)

Increase

Decrease

Detecting current with CT sensor

Diagnosing the condition of

machine and motor

Diagram 1-1 . Flow of EOCR

Reducing the down time of

systems

2. Principle

The basic principle of protecting with EOCR is very simple. The two elements we have chosen for

this are the current and the operating time. These two elements make diverse applications in

industrial field. The user using EOCR just set the suitable values of current and time after

confirming the real current of motor through using the ammeter function itself. The user just intrrupt

the power in a time expected when the current of motor overflows in motor than the user wants it.

We can think a new principle about the time expected . That is definite time, which has very simple

characteristic curve.

2

Diagram 1-2 . Structure of EOCR

Picture2-1. Inverse time characteristic Curve

Picture2-2. Definite time characteristic Curve

0.2

Motor

Contactor

A

Processor

EOCR

Output

Sensor part

At the picture above, EOCR uses definite curve of the picture2-2, whereas traditional TOR uses

Inverse curve of the picture2-1. Inverse charateristic has a reciprocal propotion curve between

current value and trip time, in which is impossible for user to set the some values. But definite

charateristic shows us that EOCR trips instantly after detecting of being over the time and current

value preset by user. Here in the definite time charateristic curve, we can see that trip time has a

quick response charateristic of 0.2sec (Ground fault , Short circuit :0.05sec). This is the merit of

electronic tech itself only and makes it possible to have the shear pin function in machine. The

flexible setting of current and trip time by user makes various applications. From now we will look

over below applications.

3. Applications upon the loads.

1) Fan, Blower

The designers select the TOR fit at the rating current of motor for their motors normally. But the fan

or blower uses only the 75~85% normal power of the rating power of motor, If the machine is

overloaded 2times by some reasons, the current will be about 1.5~1.7times of the rating current of

the motor. This means that some troubles are happening in it and we have to stop the machine and

check the system to protect it from the proceeding further problem. However, there is a enough

possibility that TOR(10 class) isn’t able to trip even untill about 4 minutes following the table 3-1

and it can be resulted in broken machine and burned motor.

3

Trip class

10A

10

20

30 9 Tp ≤ 30＜

Tripping time Tp(sec) at 7.2 times

2 Tp ≤ 10＜

4 Tp ≤ 10＜

6 Tp ≤ 20＜

A B C D

Thermal typecompensated forair temp variations

1.05 1.2 1.5 7.2

10A : 2min

10 : 4min

20 : 8min

30 :12min

Limits of operationof time- delay

Over2h

Under2h

+20 ℃

Type ofoverload relay

Multiple of current setting Referenceambient airtemperature

Table 3-1. IEC 947-4-1 for relay

However, EOCR can detect the real running current and trips the relay when the current exceed

the preset value of 1.1~1.2times in preset time that the user wants through sensing the abnormal

state of mechanical load by monitoring the current change caused by a bearing and fan blades

trouble like and can stop the motor instantly and can check it for troubles not to spread over.

Moreover, in cases of the cut belt (Idle Running), the loosened belt and the blocked filter caused by

using it for long time , it turns to the current decreasing. By monitoring on that current notify us its

fault state and the time for filter to be changed. Low current monitoring can be a good application

by use of under current protection relay function.

2) Pump system

There may be an overload and underload in pumps. If the foreign material ,specially in sewage

pump, hinder the rotation of the pump blade, the current will increase in pump and incur failed

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Picture 3-1. Blower with machine and filter trouble.

Picture 3-2. Blower with loosened belt Picture 3-3. Blower with cut belt

pump and burned motor. EOCR can check sensitively the change of current and diagnose the

mechanical state of pump whether it is normal or not. EOCR has a shear pin function to protect

pump system from stalled(jamed) state in 0.2sec of quick response. EOCR is able to notice it , if

valve or filter is blocked by monitoring undercurrent.

In submersible pump, You can protect a submersible pump having cooling effect of water from the

Dry running caused by the failed level switch . In this case has EOCR the undercurrent in motor.

EOCR can protect the system from the undercurrent as a double protection method. If the filter of

pump is blocked, the undercurret will show, then you can be informed when the filter needs to be

changed adequitely. Like pumps using the water, there is always danger to get electric shock or

ground fault . This can be protected by EOCR using the ZCT from spreading fault.

(EGR, EOCR-xxZ)

5

Picture 3-4. Pump

Discharge

LevelSwitch

Power supply

M

Picture 3-5. Sump Pump (Submersible Pump)

3) Crane , Hoist

Each Hoist and Crane has its own durable weight(load). EOCR can recognize whether the weigt is

exceeded or not, to prevent a accident may be catastrophe with instant and precise response

charateristic previously. When the weight gets to be heavy, the burden to the motor increases and

the current of motor gets to increase. If the load exceeds the rating weight of machine, it should be

stoped and restarted after lightening the load for safe and machine. However, TOR may not be

tripped for 2hours in state of 1.2 times rating current.

4) Belt Conveyer (fluctuating load)

Mechanical impact could make the designer choose the high class TOR due to thermal memory to

prevent annoying stopping. But this could make TOR hard to operate precisely because of the long

trip delay time. EOCR can monitor the state of load ,like as congested goods to convey and cut

belt ( dry running ) caused some reason, and diagnose it with current magnitude and prevent a

further spreading accident in advance.

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Picture 3-6. Crane Picture 3-7. Hoist

Conveyor

Mechanical impact !

MConveyor

5) Machine tools

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Picture 3-8. Conveyer

Motor

EOCRLT47LR97D

TORLRD

Threshold (preset)

I=0

Is=Ir

Overload

D-time Fluctuating load

Thermal memory

O-time

Start / Motor

ON

Output contact

Power Supply: A1,A2

Output contact Unwanted motor stopping

9596

98

95 96

TORIn case of above application, you cannot set Ir value as normal operation due to thermal effect. So you will have to set the value higher than normal. But in this case, TOR can not perfectly protect the motor when there is overload. Some trouble can happen to the mechanism if you are using an oversized motor .

EOCREOCR can protect well because it doesn’t have thermal memory. If overloaded , it should be tripped in preset time ( O-time).EOCR doesn’t care about oversized motor because it can be set at actual current of load by red LED and so you may not give any damage on the mechanism.

Picture 3-9. comparison between TOR and EOCR

Innumerable machine tools are used in machine industy. Kinds of drills, bites, saws, and grinders

etc., are used in machine tools as a cutting parts. CNC machine is also same as normal machine

tools. All kind of machines use a motor for processing . Here, EOCR could know the state of

machine like as overload, jam and so on and this can be done by monitoring the current of its

motor.

For example, EOCR is able to check the sharpness of drill in drilling machine. If the point of drill get

to be dull, the friction between the drill and object would get to be big and the current of motor get

rising due to increasing friction power. This dull point of drill could give an inefficient productivity.

EOCR helps you to reduce the producing defective goods.

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Picture 3-10. Drilling machine tool

Picture 3-11. CNC machine tool

Drill

Object

Picture 3-12. Example in drilling machine

6) Chemical processing motor.

This will be one example EOCR can do for chemical processing with the auto/instant reset

function of EOCR. If the machine, like an extruder, an agitator and a pump treats the liquid

materials can be hardened, stops its operating by cause of overload even the mtor has ability can

operate with its oversizing, you would need your system to be restarted prior to getting the material

hard. But TOR can not restart your system instantly before the bimetal is cooled. EOCR can restart

your system any time. Recovering the machine jamed with hardened material is time cousuming

job. You can reduce this time loss.

Another example needs constant temperature in chemical processing. They use electric heater for

heating . If the one of heating line in heater is cut by cause of long time using or some reason,

temperature will decrease and it is followed by low current. EOCR can check this low current

condition and protect this by use of EUCR. Keeping stable temperature is important issue in

chemical industry.

4. Applications upon mechanism

1) Jam Protection ( Shock relay )

When mechanical jam happens because of unexpected material in the pump mechanism or belt

conveyor ( belt, gear, etc), the motor has a peak current at the moment. The LT47 can detect if the

current is over than the set value for a preset time and it is able to break the power.

( you should set at minimum value of O-time 0.2sec).The contact of LT47 can be used for an alarm

or the breaking power by giving a signal to the coil of contactor or the shunt trip coil of circuit

breaker.

9

A

Picture 3-13. Example of Heater fault

▪ Application Object ; Extruder , Belt Conveyer , Parking machine , Machine tools

Crusher, Pump , Fan

10

M

LT47

TOR

ALARM

JAM !

Trip Command

or

or

KM1

M

EOCRLR97

LT47

JAM !

or

Trip Command

or

ALARM

KM1

How to make a setting value as a shock relay

Crusher Motor 11 kW , at 380V 22A

TOR LRD22 set at 24A

Shock relay LT47 set at 40A ~ 60A D-time setting : 4sec O-time setting : 0.2 sec (setting value depends on your need)

How to make a setting value as a shock relay

Heavy duty belt conveyer Motor 2.2kW, at 380V 5A

EOCR LR97D set at 5.5 A D-time setting : 6sec O-time setting : 5sec Shock relay LT47 set at 10A ~ 15A D-time setting : 7sec O-time setting : 0.2 sec (setting value depends on your need)

Picture 4-1. an example of application.

2) High mechanical inertia of load (long starting time)

In case of high inertia load , we get to choose a high class TOR due to long starting time. A high

class TOR has also long tripping time. If the overcurrent flows to the motor, it may make the life of

motor short or get to burn the motor because of long tripping time. But you can set the value of the

starting time and the tripping time respectively in EOCR and give a delay to the starting. If it is

overloaded in motor, you can trip the relay in preset tripping time wanted to protect its system

quickly and precisely .

▪ Typical application ; FAN , Blowers, Centrifugal machine

11

t

Ir I

Class 30

Class 20

Class 10

Typical motor starting curve with high inertiaTypical inverse curves of TOR t

Ir I

Definite

curve

D-time

setting

Adjustable

Definite

curve

O-time

setting

Adjustable

Picture 4-2. Typical TOR (LRD, LR3D)

Typical motor starting curve with high inertiaTypical inverse curves of TOR

Picture 4-3. EOCR (LR97D, LT47)

You should use class 30 TOR due to long starting time. If there is overload after starting time. The tripping time is longer than class 10 TOR , it could cause motor to overheat and burning.

EX) Blower /40HP starting time : 15-18sec TOR Class 20 Time delay Not adjustable Blower /10HP starting time : 10-12sec TOR Class 20 Time delay Not adjustable Water pump /40HP starting time : 4sec TOR Class 10 Time delay Not adjustable

According to motor specification, we can easily set the value of Ir and starting time and tripping time within setting range. The motor starting time is depending on the load. EOCR can be easily adjusted at practical starting time by D-time setting

EX) Blower /40HP starting time : 15-18sec EOCR D-time setting : 18sec O-time setting : 7sec Blower /10HP starting time : 10-12sec EOCR D-time setting : 12sec O-time setting : 6sec Water pump /40HP starting time : 4sec EOCR D-time setting : 5sec O-time setting :5sec

3) Operating cycle more than 30 to 50 cycles/hour ( frequent stop-starting )

▪ Typical application ; Hoist , Crane, Short length belt conveyer, CNC machine tools

12

t

Ir I

Class10

Typical Motor starting curve

Thermalmemorydue to

frequentstarting of

motor

t

Ir I

Definite curveD-time setting

Adjustale from

0.5sec-30sec

Definite curveO-time setting

Adjustale from

0.2sec-10sec

Typical Motor starting curve

Definite curve of EOCR

Motor

EOCRLT47LR97D

TORLRD

Threshold (preset)

I=0

Overload

D-time

Frequent motor starting

Thermal memory

O-time

Start / Motor

ON

Output contact

Power Supply: A1,A2

Output contact Unwanted motor stopping

9596

98

95 96

Is=Ir

Picture 4-4. Typical TOR (LRD, LR3D) Picture 4-5. EOCR (LR97D, LT47)

13

TORIn this kind of application, you cannot set the value of TOR as normal operation due to thermal effect ,so you should set higher value.TOR could not perfectly protect the motor if the system is overloaded

EOCREOCR can protect well because it doesn’t have thermal memory. If overloaded , it should be tripped in preset time ( O-time).

Picture 4-6. Frequent stop-starting chart