Ratioing Current Transformers - ETI PI-800 Instruction Manual

Electrical Test Instruments PI-800 and PI-1600
Section IV - Operating Instructions
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RATIOING CURRENT TRANSFORMERS

To conduct a ratio test on a current transformer, a good multi-range bench
ammeter is required in addition to the breaker test set. The breaker test set
supplies primary current to the transformer and the bench ammeter is used
to read the transformer secondary current. It is suggested that a graph of the
test results be plotted. Primary current should be the abscissa and corre-
sponding secondary current the ordinate of the graph.
WARNING: It is extremely important that the secondary circuit of the current
transformer never be broken or opened while the primary circuit is energized.
Should the secondary circuit of an energized current transformer be opened,
the collapsing magnetic field generates an extremely high voltage across the
open ends of the circuit until the resultant arc is extinguished. Under these
conditions, personal injury and/or damage to the current transformer under
test are probable.
1. Follow steps 1 through 17 in pre-test installation and setup, as required, to
set up the breaker test set.
2. Connect the current transformer primary terminals to the breaker test set
common terminal and the proper output tap terminal.
3. Connect the current transformer secondary terminals to the bench amme-
ter.
4. Set the MAC-21 to N.O. mode. Set MAINTAIN on.
5. Press and release INITIATE button; CLOSE or OUTPUT ON light should
glow, timer should operate, and current should indicate on display.
6. Adjust OUTPUT CONTROL higher until the desired current transformer pri-
mary current is read on the MAC-21 ammeter. Adjust OUTPUT TAP switch,
if necessary, to obtain required current.
7. Read and record the readings on both the breaker test set (MAC-21) and
the bench ammeter.
8. Repeat steps 6 and 7 until the desired number of test points have been ob-
tained. Note: It is suggested that test points be obtained in multiples of the
current transformer rating. For instance, for a 200/5 current transformer,
test points would be obtained at primary currents of 200, 400, 600, 800
amperes, etc.
9. Shut down test set, disconnect CT, and prepare for subsequent testing or
relocation according to steps 19 through 23 in pre-test installation and
setup outlined above.
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