SOLUTION

A transformer has negative voltage regulation when its load power factor is Leading.

Voltage regulation is the change in secondary terminal voltage from no load to full load at a specific power factor of load and the change is expressed in percentage.

E2 = no-load secondary voltage

V2 = full load secondary voltage

Voltage regulation for the transformer is given by the ratio of change in secondary terminal voltage from no load to full load to no load secondary voltage.

Voltage regulation = $\frac{{{E_2} – {V_2}}}{{{E_2}}}$

It can also be expressed as,

Regulation = $\frac{{{I_2}{R_{02}}\cos {\phi _2} \pm {I_2}{X_{02}}\sin {\phi _2}}}{{{E_2}}}$

Regulation depends on the leakage impedance of the transformer and on the power factor of the load.

A transformer has negative voltage regulation when its load power factor is Leading.

• At leading power factors, regulation is usually negative; that is, the voltage at the secondary terminals of a transformer is larger at full load than it is when the load is disconnected.
• In such cases, the equipment connected to a transformer’s secondary may be subjected to higher than rated voltages.
• This may occur when the power-factor-correction capacitor banks remain on the network while the plant operates at a reduced load.
• Also, note that for the leading power factor, if the magnitude of the phase angle φ is high, the magnitude of ${{I_2}{X_{02}}\sin \phi }$  may become greater than that of ${{I_2}{R_{02}}\cos {\phi _2}}$. The regulation then becomes negative.