NEWTON+ – Operational Manual
TRINITY
[20]
There are two problems with this:
i. Timing function is not provided from Manual control.
ii. The scheme does not work in Auto mode. The remedy is to examine the
drawings and make changes at site. The temporary remedy is to change the
relay mode to Manual, and use the panel manually. The better alternative is to
change the control wiring to incorporate suitable isolating contacts, timers etc.
to make a proper system.
CT of the Capacitor Panel itself connected to the Relay
In this case obviously the Relay does not read the power factor of the system. There
is no current through the Relay when capacitors are off. If you force one of the
capacitors on, it may cause an indication of full Lead (if the current taken by the
capacitor is sufficiently high). If the Relay is in Auto mode, it will switch off the
capacitor immediately, and nothing further will happen.
The only remedy is to disconnect the CT (short the secondary!) and bring a six core
cable from the CT of the Main Incomer. Also check that the CT rating is near the
actual full load current. Change the CT if it is too large.
Faults related to the external cabling
Only two cables originate in the panel: the Power Incomer to the panel and the CT
connections.
The power flow from the source (such as the main transformer) to the capacitor
panel as well as to the entire load must be through the bus on which the CT is
mounted. It is best to provide separate CTs for the Relay to avoid problems.
b. Faults Related to the actual site conditions:
These faults occur when the actual site conditions are different from those assumed
by the designer of the system. These faults relate to the location of the load feeders
on the busbar, buscouplers, and connections from transformers etc. The locations
of the CT are the most important factor as far as the Relay is concerned.
Another problem frequently encountered is that of insufficient load on the power
system. This might occur because the Plant has not been commissioned fully, or
because the system allows for future expansion. In either case the actual current
through the CT is very low compared to the rating of the CT.
In such conditions, the relay, (specially, if there are no small banks in the capacitor
panel) will not take any control action at all. However, the transformer losses will
cause the monthly average PF to show up as very poor. The remedy is to connect a
small bank directly (independent of the automatic control scheme) for compensating
transformer losses.
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