EMR-4000
IM02602009E
78V Vector Surge
The vector surge supervision protects synchronous generators in mains parallel operation due to very fast decoupling in
case of mains failure. Very dangerous are mains auto reclosings for synchronous generators. The mains voltage
returning typically after 300 ms can hit the generator in asynchronous position. A very fast decoupling is also
necessary in case of long time mains failures.
Generally there are two different applications.
•
Only mains parallel operation - no single operation:
In this application, the vector surge supervision protects the generator by tripping the generator circuit breaker
in case of mains failure.
•
Mains parallel operation and single operation:
For this application, the vector surge supervision trips the mains circuit breaker. Here it is insured that the
gen.-set is not blocked when it is required as an emergency set.
A very fast decoupling in case of mains failures for synchronous generators is very difficult. Voltage supervision units
cannot be used because the synchronous alternator, as well as the load impedance, support the decreasing voltage.
In this situation, the mains voltage drops only after some 100 ms below the pickup threshold of the voltage supervision
and, therefore, a safe detection of mains auto reclosings is not possible with voltage supervision only.
Frequency supervision is partially unsuitable because only a highly loaded generator decreases its speed within 100
ms. Current relays detect a fault only when short-circuit type currents exist, but cannot avoid their development. Power
relays are able to pickup within 200 ms, but they also cannot prevent the power from rising to short-circuit values.
Since power changes are also caused by sudden loaded alternators, the use of power relays can be problematic.
Whereas the vector surge supervision of the device detects mains failures within 60 ms without the restrictions
described above because it is specially designed for applications where very fast decoupling from the mains is required.
Adding the typical operating time of a circuit breaker or contactor, the total disconnection time remains below 150 ms.
Basic requirement for tripping of the generator/mains monitor is a change in load of more than 15 - 20% of the rated
load. Slow changes of the system frequency, for instance at regulating processes (adjustment of speed regulator), do
not cause the relay to trip.
Trippings can also be caused by short-circuits within the grid, because a voltage vector surge higher than the preset
value can occur. The magnitude of the voltage vector surge depends on the distance between the short-circuit and the
generator. This function is also of advantage to the Power Utility Company because the mains short-circuit capacity
and, consequently, the energy feeding the short-circuit is limited.
To prevent a possible false tripping, the vector surge measuring is blocked at a low input voltage <15% Vn. The
undervoltage lockout acts faster then the vector surge measurement.
Vector surge tripping is blocked by a phase loss so that a VT fault (e. g.: faulty VTs fuse) does not cause false tripping.
www.eaton.com
631
