Mains pro 1.6.1 Global Guide
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8.5.1 Measuring principle
When synchronous alternator is loaded, the rotor displacement angle
is built between the terminal voltage
(mains voltage)
g and the synchronous electromotive force
e. Therefore a voltage difference ΔU is built
between
e and
g. The rotor displacement angle
between stator and rotor is depending on mechanical
moving torque of the generator shaft. The mechanical shaft power is balanced with the electrical feeder mains
power and therefore the synchronous speed keeps constant.
Image 8.6 In parallel with the mains
In case of mains failure or auto reclosing the generator suddenly feeds a very high consumer load. The rotor
displacement angle is decreased repeatedly and the voltage vector
g changes its direction to
g’.
Image 8.7 At mains failure
As shown in the timing diagram the voltage jumps to another value and the phase position changes. This
procedure is called phase or vector surge. MainsPro continuously measures the cycles, starting each zero up
ward slope. The time cycle is internally compared to the reference time. In case of vector surge the zero up ward
is delayed and the device trips instantaneously. The trip angle Δ
and consequently the sensitivity of the vector
surge detection is adjustable by the setpoint
