reg 670 app

7/30/2019 REG 670 App.

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IAmpComp30 -10.000 - 10.000 % 0.001 0.000 Amplitude factor to calibrate current at

30% of Ir

IAmpComp100 -10.000 - 10.000 % 0.001 0.000 Amplitude factor to calibrate current at

100% of Ir

UAmpComp5 -10.000 - 10.000 % 0.001 0.000 Amplitude factor to calibrate voltage at

5% of Ur


30% of Ur


100% of Ur

IAngComp5 -10.000 - 10.000 Deg 0.001 0.000 Angle calibration for current at 5% of Ir



IBase 1 - 99999 A 1 3000 Base setting for current level

UBase 0.05 - 2000.00 kV 0.05 400.00 Base setting for voltage level

Mode L1, L2, L3

Arone

Pos Seq

L1L2

L2L3

L3L1

L1

L2

L3

- - Pos Seq Selection of measured current and

voltage

Negative sequence time overcurrent

protection for machines

NS2PTOC 2I2> 46I2

Negative sequence overcurrent protection for machines NS2PTOC is intended

primarily for the protection of generators against possible overheating of the rotor

caused by negative sequence component in the stator current.

The negative sequence currents in a generator may, among others, be caused by:

Section 3 1MRK 502 030-UEN AIED application

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Unbalanced loads

Line to line faults

Line to ground faults

Broken conductors

Malfunction of one or more poles of a circuit breaker or a disconnector

NS2PTOC can also be used as a backup protection, that is, to protect the generator

in the event line protections or circuit breakers fail to perform for unbalanced

system faults.

To provide an effective protection for the generator for external unbalanced

conditions, NS2PTOC is able to directly measure the negative sequence current.

NS2PTOC also have a time delay characteristic which matches the heating

characteristic of the generator I22t = K as defined in standard.

where:

I2 is negative sequence current expressed in per unit of the rated generator current

t is operating time in seconds

K is a constant which depends of the generators size and design

A wide range of I22t settings is available, which provide the sensitivity and

capability necessary to detect and trip for negative sequence currents down to the

continuous capability of a generator.

A separate output is available as an alarm feature to warn the operator of apotentially dangerous situation.

Negative-sequence time overcurrent protection NS2PTOC is designed to provide a

reliable protection for generators of all types and sizes against the effect of

unbalanced system conditions.

The following features are available:

Two steps, independently adjustable, with separate tripping outputs.

Sensitive protection, capable of detecting and tripping for negative sequence

currents down to 3% of rated generator current with high accuracy. Two time delay characteristics for step 1:

Definite time delay

Inverse time delay

The inverse time overcurrent characteristic matches

22I t K= capability curve

of the generators.

Wide range of settings for generator capability constant Kis provided, from 1

to 99 seconds, as this constant may vary greatly with the type of generator.

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Minimum operate time delay for inverse time characteristic, freely settable.

This setting assures appropriate coordination with, for example, line protections.

Maximum operate time delay for inverse time characteristic, freely settable.

Inverse reset characteristic which approximates generator rotor cooling rates

and provides reduced operate time if an unbalance reoccurs before the

protection resets.

Service value that is, measured negative sequence current value, in primary

Amperes, is available through the local HMI.

During unbalanced loading, negative sequence current flows in the stator winding.

Negative sequence current in the stator winding will induce double frequency

current in the rotor surface and cause heating in almost all parts of the generator rotor.

When the negative sequence current increases beyond the generators continuous

unbalance current capability, the rotor temperature will increase. If the generator is

not tripped, a rotor failure may occur. Therefore, industry standards has been

established that determine generator continuous and short-time unbalanced current

capabilities in terms of negative sequence current I2 and rotor heating criteria2

2I t .

Typical short-time capability (referred to as unbalanced fault capability) expressed

in terms of rotor heating criterion2

2I t K= is shown below in Table 103.

[ ]2

2I t K s=

Salient pole generator 40

Synchronous condenser 30

Cylindrical rotor generators: Indirectly cooled 30

Directly cooled (0 800 MVA) 10

Directly cooled (801 1600

MVA)

See Figure 119

Fig 119 shows a graphical representation of the relationship between generator

22I t capability and generator MVA rating for directly cooled (conductor cooled)

generators. For example, a 500 MVA generator would have K = 10 seconds and a

1600 MVA generator would have K = 5 seconds. Unbalanced short-time negative

sequence current I2 is expressed in per unit of rated generator current and time t in

seconds.


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en08000358.vsd

IEC08000358 V1 EN

Figure 119: Short-time unbalanced current capability of direct cooled generators

Continuous I2 - capability of generators is also covered by the standard. Table 104

below (from ANSI standard C50.13) contains the suggested capability:

Salient Pole

with damper winding 10

without damper winding 5

Cylindrical Rotor

Indirectly cooled 10

Directly cooled

to 960 MVA 8

961 to 1200 MVA 6

1201 to 1500 MVA 5

As it is described in the table above that the continuous negative sequence current

capability of the generator is in range of 5% to 10% of the rated generator current.

During an open conductor or open generator breaker pole condition, the negative

sequence current can be in the range of 10% to 30% of the rated generator current.

Other generator or system protections will not usually detect this condition and the

only protection is the negative sequence overcurrent protection.

Inducing of negative sequence current in a generator can result from any system

unbalance and these, in turn, may be caused by:

Unbalanced loads such as

Single phase railroad load

Unbalanced system faults such as


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Line to earth faults

Double line to earth faults

Line to line faults

Open conductors, includes Broken line conductors

Malfunction of one pole of a circuit breaker

.

When inverse time overcurrent characteristic is selected, the

operate time of the stage will be the sum of the inverse time delayand the set definite time delay. Thus, if only the inverse time delay

is required, it is of utmost importance to set the definite time delay

for that stage to zero.

Negative sequence time overcurrent protection for machines NS2PTOC provides

two operating time delay characteristics for step 1:

Definite time delay characteristic

Inverse time delay characteristic

The desired operate time delay characteristic is selected by setting CurveType1 as

follows:

CurveType1 = Definite

CurveType1 = Inverse

Step 2 always has a definite time delay characteristic. Definite time delay is

independent of the magnitude of the negative sequence current once the start value

is exceeded, while inverse time delay characteristic do depend on the magnitude of

the negative sequence current.

This means that inverse time delay is long for a small overcurrent and becomes

progressively shorter as the magnitude of the negative sequence current increases.

Inverse time delay characteristic of the NS2PTOC function is represented in the

equation2

2I t K= , where the K1 setting is adjustable over the range of1 99

seconds. A typical inverse time overcurrent curve is shown in Figure 120.


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Negative sequence inverse time characteristic

Negative sequence current

Timedelay

I2

tMax

tMin

IEC08000355-2-en.vsd

1

10

100

1000

10000

0.01 0.1 1 10 100

IEC08000355 V2 EN

Figure 120: Inverse Time Delay characteristic

The example in figure 120 indicates that the protection function has a set minimum

operating time t1Min of 5 sec. The setting t1Min is freely settable and is used as a

security measure. This minimum setting assures appropriate coordination with forexample line protections. It is also possible to set the upper time limit, t1Max.

The trip start levels Current I2-1> and I2-2> of NS2PTOC are freely settable over

a range of 3 to 500 % of rated generator current IBase. The wide range of start

setting is required in order to be able to protect generators of different types and sizes.

After start, a certain hysteresis is used before resetting NS2PTOC. For both steps

the reset ratio is 0.97.

The alarm function is operated by START signal and used to warn the operator for

an abnormal situation, for example, when generator continuous negative sequence

current capability is exceeded, thereby allowing corrective action to be taken

before removing the generator from service. A settable time delay tAlarm is

provided for the alarm function to avoid false alarms during short-time unbalanced

conditions.


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Operation Off

On

- - Off Operation Off / On

IBase 1 - 99999 A 1 3000 Rated generator current in primary

Amperes

tAlarm 0.00 - 6000.00 s 0.01 3.00 Time delay for Alarm (operated by

START signal), in sec

OpStep1 Off

On

- - On Enable execution of step 1

I2-1> 3 - 500 %IB 1 10 Step 1 Neg. Seq. Current pickup level, in

% of IBase

CurveType1 Definite

Inverse

- - Definite Selection of definite or inverse time-

characteri. for step 1

t1 0.00 - 6000.00 s 0.01 10.00 Definite time delay for trip of step 1, in sec

tResetDef1 0.000 - 60.000 s 0.001 0.000 Time delay for reset of definite timer of

step 1, in sec

K1 1.0 - 99.0 s 0.1 10.0 Neg. seq. capability value of generator

for step 1, in sec

t1Min 0.000 - 60.000 s 0.001 5.000 Minimum trip time for inverse delay of

step 1, in sec

t1Max 0.00 - 6000.00 s 0.01 1000.00 Maximum trip delay for step 1, in sec

ResetMultip1 0.01 - 20.00 - 0.01 1.00 Reset multiplier for K1, defines reset

time of inverse curve

OpStep2 Off

On

- - On Enable execution of step 2

I2-2> 3 - 500 %IB 1 10 Step 2 Neg. Seq. Current pickup level, in

% of IBase

CurveType2 Definite

Inverse

- - Definite Selection of definite or inverse time-

characteri. for step 2

t2 0.00 - 6000.00 s 0.01 10.00 Definite time delay for trip of step 2, in sec

tResetDef2 0.000 - 60.000 s 0.001 0.000 Time delay for reset of definite timer of

step 2, in sec

K2 1.0 - 99.0 s 0.1 10.0 Neg. seq. capability value of generator

for step 2, in sec

t2Min 0.000 - 60.000 s 0.001 5.000 Minimum trip time for inverse delay of

step 2, in sec

t2Max 0.00 - 6000.00 s 0.01 1000.00 Maximum trip delay for step 2, in sec

ResetMultip2 0.01 - 20.00 - 0.01 1.00 Reset multiplier for K2, defines reset

time of inverse curve


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