MAGNETIC BALACE TEST

Magnetic Balance test used to find the distribution of Flux (Magnetic), Core Assembly Condition and defect in winding (If any).

It may check at HV Side or LV Side as per requirement/ site condition.

For Star Connection, apply the supply at U & N measure the values at V & N as well as W & N, then repeat the apply at V & N measure other two values, repeat it to apply at W & N.

For Delta connections, apply voltage must be in Phase - Phase like U & V, V & W and W & U.

For Ex:

U & N = (V & N) + (W & N); 240 = 198 + 42

Example : Results of 16 MVA, 110/ 33 KV Transformer, Vector Group of Dyn 11 (Delta Star 11)

Magnetic Balance at HV side

1U - 1V 1V - 1W 1W - 1U

417.0 (Appl) 401.0 22.0

232.0 419.0 (Appl) 189.0

20.0 402 420 (Appl)

Magnetic Balance at LV Side:

2u - 2n 2v - 2n 2w - 2n

238 (App) 208 31

122 241 (App) 119

38 207 245 (App)

RATIO TEST

Calculating the Specified Ratio:

If Star – Star Transformer: Ratio K = HV Specified voltage / LV Specified Voltage

If Delta – Star Transformer: Ratio K = 1.732 * (HV Specified voltage / LV Specified Voltage)

If Delta – Delta Transformer: Ratio K = HV Specified voltage / LV Specified Voltage

Procedure:

1. In Ratio Meter just rotate the dial and directly measure the value.

2. By apply separate voltage and measure using Meters.

i) Apply Single Phase/ phase to Phase/ All three phases as per availability. Measure the output.

ii) For easy reference apply 2 phase, that means 1st U & V,2nd V & W, finally W & U.

iii) The output must be V out = Applied voltage/ Specified Ratio (K)

Error:

Calculating the error is E = Specified Ratio ± Measured Ratio

( +) % Error = (100 * (Specified Value/Measured value)) – 100

( - ) % Error = (100 * (Measured value/ Specified Value)) – 100

Posted By: B.K, boopathymail@gmail.com, transtechindia33@gmail.com