METHOD FOR MEASURING ACTIVE RESISTANCES TO DIRECT CURRENT WINDINGS OF A POWER TRANSFORMER Russian patent published in 2019 - IPC G01R27/00 

FIELD: measuring equipment.

SUBSTANCE: invention relates to electrical measurements and can be used in operation, repair or drying of transformers. Method of measuring resistance to direct current of power transformer windings includes measuring current and voltage and determining resistance on primary winding. At the same time the secondary winding is short-circuited, the primary winding is connected to the DC voltage source through the circuit containing an ammeter, a voltmeter and voltage polarity switch on the winding, and transformer is connected to constant voltage source to steady state. Steady-state voltage U and primary winding current I are then measured and determine the primary resistance of the primary winding r₁, then voltage polarity switch on the winding instantaneously changes voltage polarity on primary winding and at design moment of time from beginning of new transient process, which is determined by formula: where i₀₀ is initial current of primary winding in fractions of steady-state current in this winding at specified voltage (i₀₀=I_0(-)/I), where I_0(-) – measured current at initial moment after switching of source polarity; 1/p₁ – maximum time constant of transient process at constant voltage supplied to primary winding at short-circuited secondary winding, which is found by formula:

where U_rph – rated phase voltage of primary winding of transformer; U_s – source voltage at idling; U is the steady-state voltage on the primary winding during measurement; I₀ is the primary winding idling current; ƒ_r is rated frequency of transformer; r_1p, r'_2p – rated resistances of primary and secondary windings, and measuring instantaneous voltage values U_mes and current I_mes primary winding, then total value r active resistances of primary r₁ and reduced secondary windings r'₂ (r=r₁+r'₂) ratio r = U_mes/I_mes; resistance r'₂ is determined by formula r'₂=r-r'₁; intrinsic resistance of the secondary winding is determined as r₂=r'₂/k², where k is transformation coefficient of phase voltages.

EFFECT: reduced labor intensiveness of measurement of active resistance of transformer windings.

1 cl, 1 dwg