This Excel spreadsheet presents the simulation of the UR T60/T35 transformer biased differential protection and is built to provide customers,

with a tool for excersizing different transformer setups, and test scenarios. The simulation can be used to verify the biased differential settings, the differential

and restraint metering on the relay, and the correct operation of the element, under created test conditions.

Some rules to follow, when working with the simulation program:

1) Please make sure you enter settings or test currents only into the clear boxes on the spreadsheet provided for that!

2) Make sure you enter "0" MVA for all windings you don't use in your transformer setup menu.

3) Make sure the angle of Winding 1 is "0" and the angles of the other transformer windings are entered With Respect To (WRT) Winding 1 as negative angl

4) Make the settings for the Differential/Restraint characteristic without exceeding their ranges as set on the relay.

5) The magnitudes and angles of the injected test currents should be entered as the ones normally received by the relay from the transformer winding CTs.

This means for example, that if we have transformer 100MVA, 230kV/69kV Y/D30 degrees, and CT(w1) 500:5, and CT(w2) 1000:5, and we want to

simulate balanced conditions(differential current = 0), one can make the transformer setup, and enter the test currents for Winding 1 and Winding 2 as .

shown on the picture bellow:

Note that the angles of the entered test currents for Winding 2, are as they are received and seen

by the relay in normal in service conditions, means adding 180 degreese to the phase shift angle of th

power transformer. From the example above, the angles say for phase A of Winding 2 than will be

-30 -180 = -210 degrees, phB(W2) = - 150-180 =330, and for ph C(W2) = - 270-180 = -90 degree

 

 

s.

 

 

  TRANSFORMER SETTINGS AND CTs

Nomber of Windings: 3   DIFF / RSTR CHARACTERISTIC

W1 W2 W3 W4 W5 W6   DIFFERENTIAL- RESTRAINT GRAPH

Rated(MVA) 100 50 50 0 0 0 Diff. min. PKP 0.20 Slope1 35.0

Nom. (kV) 115 13.8 13.8 0.48 0.48 69 Kneepoint 1 2.00

Connection WYE DELTA DELTA WYE WYE WYE Kneepoint 2 4.00 Slope2 95.0

Grounding  YES NO NO  YES YES YES

 Angle WRT 0 -30 -30 0 0 0 Pre-calculated graph points >>Pre-calculated ratio of the point from the

CT primary 1000 3000 3000 3000 3000 1000 Id/Ir, (%) Ph A Ph B Ph C characteristic, corresponding to the same

CT sec. tap 5 5 5 5 5 5 35.0 35.0 35.0 restraint as per the actual Id/Ir ratio. The trip

Inom. Prim. 502.0 2091.8 2091.8 0.0 0.0 0.0   occurs, when the actual Id/Ir ratio,(%) is bigger Inom.Sec. 2.510 3.486 3.486 0.000 0.000 0.000   than the pre-calculated Id/Ir ratio, (%)

Rotations ABC 2   ACTUAL VALUES  TEST CURRENTS Magnitude Ref. Winding #: 2

IA IB IC

W1 DIFFERENTIAL CURRENTS

Magnitude 2.51 2.51 2.51 Iad Ibd Icd

Angle 0.0 -120.0 -240.0 Magnitude 0.00 0.00 0.00

W2  Angle -30.0 -150.0 -270.0

Magnitude 3.49 3.49 3.49

Angle -210.0 -330.0 -90.0 RESTRAINT CURRENTS

W3 Iar  Ibr  Icr 

Magnitude 3.49 3.49 3.49 Magnitude 1.39 1.39 1.39

Angle -210.0 -330.0 -90.0

W4 Actual Differential/Restraint Ratio

Magnitude 0.00 0.00 0.00  Actual ph A % ph B % ph C %

Angle -180.0 -300.0 -60.0 Id/Ir ratio 0.0 0.0 0.0

W5

Magnitude 0.00 0.00 0.00 DIFF. OPERATION

Angle -180.0 -300.0 -60.0 NO TRIP

W6 Ia Ib Ic

Magnitude 0.00 0.00 0.00 No trip No trip No trip

Angle 0.0 0.0 0.0

magn. Ref. Winding 0

WYE NO ABC 1 auto

DELTA YES ACB 2 1

ZIG-ZAG 3 2

4 3

5 4

6 5

6

Select Magnitude Ref. Winding:

0

1

2

3

4

5

6

7

8

9

10

11

12

0 1 2 3 4 5 6 7 8 9 10 11 12

I diff, pu

I restr, pu

Operating Characteristic

Slope characteristics Iad Ibd Icd