Field tests of new instruments at Irkutsk Hydroelectric Power Station

6 august 2015

At the end of July field tests of a new microhmmeter MIKO-21 were carried out on Irkutsk Hydroelectric Power Station High-Voltage Electric Equipment Site.

In high voltage equipment stock of Irkutsk Hydroelectric Power Station there are modern ALSTOM sulfur-hexafluoride (SF6) dead tank circuit breakers, which are characterized by built-in transformers that make accurate measurement of transfer resistances of circuit breaker contact combination difficult.

In order to solve this task, specialists of SKB EP implemented additional specialized operation modes in new Microhmmeter MIKO-21, in operation of which inductance of current transformers is considered. Let us present the results of circuit breaker contact transfer resistances measurements summarized in the Table:

Type of circuit breaker ALSTOM HGF-1012, 110 kV
Measurement Mode	Test Current	Phase A	Phase B	Phase C
"Mode 1"	10 А	269.94 µOhm	279.51 µOhm	276.54 µOhm
"Mode 1"	50 А	269.73 µOhm	294.69 µOhm	300.61 µOhm
"Mode 1"	100 А	269.67 µOhm	299.73 µOhm	310.65 µOhm
"Mode 1"	200 А	269.56 µOhm	299.89 µOhm	311.01 µOhm
"Mode 2 with CT"	200 А	91.760 µOhm	93.403 µOhm	98.941 µOhm
"Mode 2 with CT"	100 А	90.808 µOhm	93.306 µOhm	88.133 µOhm
"Mode 2 with CT"	200 А	90.781 µOhm	93.348 µOhm	88.151 µOhm

Note: "Mode 1" – measurements without in-built circuit transformers and for all permanent and demountable joints; "Mode 2 with CT" – measurements with in-built circuit transformers with use of energy saving; "Mode 3 with CT" - measurements with in-built circuit transformers, but at maximum measuring current duration and without use of algorithms of energy saving

As is seen from the given example, the readings of customary mode of microhmmeter differ from the readings in special measurement modes nearly three times with measurement in customary mode derating circuit breaker resistance, which indicates measurement inefficiency without special adjustment to this type of equipment.

Apart from that, new microhmmeter is absolutely self-contained. In order to increase output capacity MIKO-21 has a new type of accumulator, that enables to use the instrument in a more mobile manner for repeated and continuous measurements, which is especially convenient when using the instrument at height (e.g., from elevating equipment).

This instrument characteristic enabled to carry out measurements in all modes with one accumulator charge during the tests not only of the circuit breaker itself, but also of all contacts of adjacent disconnecting switch (RDZ-1-110/2000).

When inspecting resistance of disconnecting switch earting blade contacts exceedance of two phases was revealed: А=83.5 µOhm, В=280 µOhm, С=259.39 µOhm. At visual inspection of earthing blades there was revealed a gap of moving contact pieces, which require adjustment with the help of pull-up bolts. After retorque of pins of earth moving contact piece the blades resistance was normalized: А=83.75 µOhm, В=87.788 µOhm, С=91.696 µOhm.

We express our gratitude to the employees of Irkutsk Hydroelectric Power Station who have participated in these test works

The tests have been successful and productive, which confirms the comments about operation practice with MIKO-21 instruments from the Supervisor of Electric Equipment Operation Site of Irkutsk Hydroelectric Power Station – Oleg Nikolayevich Kosyanenko:

Reference to a video on SKB EP Youtube channel: https://youtu.be/ACN6A0NZ2yg