The following IT secondary readings were taken at a new digital feeder protection panel in a utility application. The CT is 300:5 and the power system is nominal 25000V with a PT = 14400/120 V. Both ITs are wye connected. Phase rotation = RWB.

Ir = 1.18 A -22 Vrn= 116.0 V 1

Iw = 1.18 A -142 Vwn= 116.5 V -118

Ib = 1.19 A +97 Vbn= 116.8 V +120

1. Plot the secondary voltage and current phasors on a phasor diagram. Ensure the diagram is neat, lines are straight, magnitudes and angles to scale, and all required diagram labelling is present.

2. Calculate the primary Phase current, Phase to neutral and Phase to Phase voltages, Total kW, kVAR and kVA. Include magnitudes and phase angles. Show your work.

Ir = Vrn= Vrw=

Iw= Vwn= Vwb=

Ib= Vbn= Vbr=

Total kW=

Total kVAR=

Total kVA=

3. Plot the Question 2 data to scale on a PQ diagram for one phase. Correctly label the primary W, VAR, VA and phase angle.

4. Some time later the data below was recorded in the control room for the same feeder.

- What differences can be observed ?

- Is the relay data reliable ?

- Assuming correct equipment installation, what could account for the differences ?

Data displayed in Control Room:

Ir= 66.6 A -24.8 Iw= 66.5 A -144 Ib= 66.5 A +95

Vr= 14274 V Vw= 14325 V Vb= 14379 V

3P = 2593 kW

3Q= 1207 kVAR

Pf = 0.906 lag