# Transformers Questions and Answers – Sumpner’s Test

This set of Transformers Multiple Choice Questions & Answers (MCQs) focuses on “Sumpner’s Test”.

1. Sumpner’s test is conducted on transformers to study effect of ____________
a) Temperature
b) Stray losses
c) All-day efficiency
d) Cannot be determined

Explanation: Sumpner’s test is the test which is used to determine the steady temperature rise if the transformer was fully loaded continuously; this is so because under each of these tests the power loss to which the transformer is subjected is either the core-loss or copper-loss but not both.

2. Which of the following tests are enough to find all the parameters related to a transformer?
a) OC test
b) OC, SC test
c) OC, SC, Sumpner’s test
d) Sumpner’s test

Explanation: While OC and SC tests on a transformer yield its equivalent circuit parameters, these cannot be used for the ‘heat run’ test wherein the purpose is to determine the steady temperature rise if the transformer was fully loaded continuously.

3. Sumpner’s test is performed on _________
a) Single transformer at a time
b) Only two transformers at a time
c) Minimum 2 transformers at a time
d) Many transformers at a time

Explanation: Sumpner’s test is used to determine the effect of transformer on loaded condition. Thus, two transformers are tested simultaneously, where one simply acts as a load to another transformer.

4. In Sumpner’s test __________
a) Primaries can be connected in either way
b) Primaries are connected in parallel with each other
c) Primaries of both transformers are connected in series with each other
d) No need to connect primaries

Explanation: Sumpner’s test is also called as back-to-back test, where two transformers are used where one transformer acts as a load to another transformer. Primaries of both of the transformers used in a test, are connected in parallel with each other.

5. Which test is sufficient for efficiency of two identical transformers under load conditions?
a) Short-circuit test
b) Back-to-back test
c) Open circuit test
d) Any of the above

Explanation: Open circuit test and short circuit test collectively gives the value of all parameters of an equivalent circuit of a transformer. While Sumpner’s back-to-back test gives the heat run effect of machine by considering rise in temperature.
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6. In Sumpner’s test _____________
a) Two secondaries are connected in phase opposition
b) Two secondaries are connected in phase addition
c) Can be connected in either way
d) Never connected with each other

Explanation: In conducting Sumpner’s test two primaries are connected in parallel to the rated voltage supply and secondaries are connected in phase opposition. For the secondaries to be in phase opposition rated secondary voltage across the terminals to be zero.

7. When secondaries are connected in phase opposition, power drawn by the circuit is equal to ___________
a) 2*Pi
b) Pi2
c) Pi
d) 2*Pc

Explanation: If V2 source is assumed shorted, the two transformers appear in open circuit to source V1 as their secondaries are in phase opposition and therefore no current can flow in them. The current drawn from source V1 is thus 2I0 and power is 2P0 = 2Pi, twice the core-loss of each transformer.

8.When the AC supply at the primary side of a transformer are shorted, power drawn by the circuit is equal to ___________
a) 2*PC
b) 2*Pi
c) 2*PC + 2*Pi
d) Can’t be determined

Explanation: When the ac supply (10) terminals are shorted, the transformers are series-connected across V2 supply and are short-circuited on the side of primaries. Therefore, the impedance seen at V2 is 2Z and when V2 is adjusted to circulate full-load current (Ifl), the power fed in is 2PC (twice the full-load copper-loss of each transformer).

9.Total power required for Sumpner’s test is given by ________
a) PC + Pi
b) PC + 2Pi
c) 2PC + Pi
d) 2(PC + Pi)

Explanation: In the Sumpner’s test while the transformers are not supplying any load, full iron-loss occurs in their cores and full copper-loss occurs in their windings; net power input to the transformers being (2P0 + 2Pc). The heat run test could, therefore, be conducted on the two transformers, while only losses are supplied.

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