Iec Curves for Oc, Ef Fault Relays

4) TMS or 10I/Is settings  In SEPAM, the IDMT characteristic curve is also derived from the formula that complies with the BS142 and IEC 60255 standards. It is mathematically mathematically defined as

T d d (s) = 

T 

K  ( Is  ) -1

X  ( β  )

I  α

where  Td = opera operating ting time in s   T = operation time at 10Is, Is = primary threshold current current in A or kA I = primary actual current value in A or kA α Κ  and β are constants. ,

Similarly, by varying the α and K values in the same formula, it leads to four standard curves.

Table 2. Values of α Κ  and β which determine the degree of inversian of the IDMT curve ,

Type of curve Normally inverse Very Inverse Extremely Inverse Long-time Inverse

α 0.02 1.0 2.0 1.0

Κ  0.14 13.5 80.0 120.0

β 2.97 1.5 0.808 13.33

In comparison with the earlier formula based on TMS, the relationship is T/ β = TMS. This is because the time delay   T is the operation time of the relay when the current reaches 10Is. Hence, the time delay of the IDMT tripping may be set either by: I I

The Difference Between Type 1 And Type 1.2 IDMT Curves It is important to distinguish the difference in the initial pick up of the various types of IDMT curves.

Type of curve

Type

Standard inverse time (SIT) Very inverse time (VIT or LTI) Extremely inverse time (EIT) Ultra invers inverse e time (UIT) RI curve IEC IE C st stan anda dard rd in inve vers rse e ti time me SI SIT/ T/A A IEC ver veryy inve inverse rse tim time e VIT or LTI/B IEC ext extrem remely ely inv invers erse e tim time e EIT EIT/C /C IEEE IE EE mo mode dera rate tely ly in inve vers rse e (I (IEC EC/D /D)) IEEE very inverse (IEC/E) IEEE extremely inverse (IEC/F) IAC inverse IAC very inverse IAC extremely inverse

1.2 1.2 1.2 1.2 1 1 1 1 1 1 1 1 1 1

The curve equations are given in the chapter entitled "IDMT protection functions" 

Figure 2 Type of IDMT curves

Figure 2 shows that there are Type 1 and Type 1.2 characteristic curves in SEPAM. SEPAM. For instance, under the SI curve, there is the SIT, which is based on Type 1.2 characteristic. The other is the SIT/A, which is based on  Type  T ype 1 characteristic.

Type 1

t

Type 1.2

T (s): operation time at 10Is or TMS: where TMS = T/ β

Example: For 100/ 5 CT with P.S P.S at 100%, TMS=0.1, using the  standard inverse 3/10 curve, the SEPAM relay will be set  based on the following:  Is = 100A Type of curve =SIT/A If the setting mode is set as 10I/Is then  T= β X TMS = 2.97 X 0.1 = 0.297. If the setting mode is set as TMS, then TMS will be set  at 0.1. With a primary current of 200A passing through the relay, both modes will provide the same tripping time :  At 10I/Is mode: d (s) T d  (s) = 

0.14  X (0.297/2.97) = 1s  (200/100)0.02  -1

0.14  (2)0.02 -1

1

1.2

10

20

Ms

Figure 3. IDMT curves base d on Type Type 1 and Type 1.2

Figure 3 shows that for the Type 1 curve, the relay will activate at 1  X Is, after a certain time delay. However, for  Type  T ype 1.2 curve, the relay will only activate at 1.2  X Is. The  Type 1.2 curve characteristic is in accordance with BS 142 standard, which has considered the nature of the electromechanical relay. With a better understanding of  the IDMT curves and the way the SEPAM relay interprets the curves, SEPAM users will better appreciate the flexibility of the settings for phase over-current (51) protections. Contributed by:  Tong Ween Kai  Assistant Marketing Manager MV/LV Equipment

 At TMS mode:

T(s) = 

T

X 0.1 = 1s 

REFERENCES Electrical Network Protection, SEPAM Series 20 User Manual. Electrical Network Protection, Protection Guide.

09

2.4 OVERCURRENT ELEMENTS

2 PRODUCT DESCRIPTION

2.4OVERCURRENT ELEMENTS 2.4.1 PHASE TIME OVERCURR OVERCURRENT ENT ELEMENT (51P)DIFFERENTIAL UNITS (87-1) (87-2) A Phase Time Overcurrent unit is provided in the relay. There are three possibilities for the curve selection, depending on the selected model. IEC curves comply with the criteria specified in the IEC255-4 Standard Standard and British Standard BS142 ANSI curves comply with ANSI C37.90 standards IAC curves simulate the behaviour of GE IAC relays. A time dial can be applied to any of these curves to optimize co-ordination with other d evices in the net. Additionally, there is a possibility to define a User’s Curve, which can be used for both three-phase overcurrent and ground elements. In order to avoid undesired trips, time overcurrent elements will not pickup till a value of 1.05 * Set value. Due to design criteria, actual pickup level has been INTENTIONALLY INTENTIONALLY set to +5% over the set value to ensure that even in the worst case scenario the relay will NEVER TRIP under the intended setting.This meets IEC international standards.

2.4.1.1 IEC CURVES  The general formula for IEC/BS142 curves is as follows:

Where: CURVE NAME

A

P

Q

B

K

Mod Inverse (IEC Curve A)

0.14

0.02

1

0

0

Very Inverse (IEC Curve B)

13.5

Extremely Inverse (IEC Curve C) 80 80

1

1

0

0

2

1

0

0

D =Time Dial setting (set in the relay by user). V = I / Ipickup setting > 1.05

2.4.1.2 ANSI CURVES  The general formula for all ANSI curves is as follows:

Where: CURVE NAME

A

B

C

D

E

Inverse

0.0274

2.2614

0.3000

-4.1899

9.1272

Very Inverse

0.0615

0.7989

0.3400

-0.2840

4.0505

Extremely In Inverse

0.0399

0.2294

0.5000

3.0094

0.7222

M =Time Dial setting (set in the relay by user). V = I / Ipickup setting > 1.05

2-4

MIFII Digital Feeder Relay

GEK-106237P  

2 PRODUCT DESCRIPTION

2.4 OVERCURRENT ELEMENTS

2.4.1.3 IAC CURVES 

The general formula of IAC Curve is as follows:

2

Where: TDM: Time Dial Multiplier (Set in the Relay by User) I / Ipickup setting > 1.05

2.4.1.4 USER CURVES  The general formula for the user curve is as follows:

Where:

D

=Time Dial setting (set in the relay by user).

V

=I / Ipickup setting > 1.05

I

=Input Current

T

=Operate Time (sec.)

A, P, Q, B, K

=Constants defined in the standard, as follows:

PARAMETERS

A

B

P

O

K

Range

0 – 125

0-3

0-3

0-2

0-1.999

Step

0.001

0.001

0.001

0.001

0.001

Unit

Sec.

Sec.

NA

NA

Sec.

Default value

0.05

0

0.04

1

0

Settings available for the phase time overcurrent unit allows the user to: enable/disable the unit; set the pickup value (between 0.1 – 2.4 times the rated current in case of 1/5 A ground, or 0.005-0.12 A in case of sensitive ground) and set the current/time operating characteristic (type and time dial).

Note: The relay will use either IEC, IAC or ANSI curves, depending on the model. Refer to Appendix B for a deeper explanation of the curves.

GEK-106237P

MIFII Digital Feeder Relay

2-5  

2.4 OVERCURRENT ELEMENTS

2 PRODUCT DESCRIPTION 2.4.2 PHASE(50P1, 50P2)

MIFII provides 2 phase instantaneous overcurrent elements, 50P1 (‘H’ for high pickup) and 50P2 (‘L’ for low pickup). Each one can be enabled/disabled and set independently. Settings from these elements allow to set the pickup value from 0.1 to 30 times the rated current, and the time delay from 0.00 to 6 00.00 seconds. 2.4.3 GROUND TIME OVERCURRENT ELEMENT (51G) The Ground Time Overcurrent element offers the same setting possibilities as the Phase Time Overcurrent element. The ground current can be obtained from a residual connection on the CTs. For a more sensitive ground current detection, a window type (zero sequence) CT, taking the three phases inside its windows can be used. Refer to figure 3-6 for more details. 2.4.4 GROUND INSTANTANEOUS OVERCURRENT ELEMENTS (50G1, 50G2) The MIFII relay provides 2 Ground Instantaneous Overcurrent Elements, 50G1 (‘1’ for High pickup) and 50G2 (‘2’ for Low pickup). Settings and ranges available for these elements are the same ones described for the Phase Instantaneous Overcurrent Elements, 50P1 and 50P2.

2-6

MIFII Digital Feeder Relay

GEK-106237P  

APPENDIX B

B.1 IEC/BS142 CURVES

APPENDIX B TIME-CURRENT CURVES FOR 51P AND 51N UNITSB.1IEC/BS142 CURVES

For 1 < V