1.0 CONNECTION TO SUPPLY
1.1 Installation
must only be carried out by suitably qualified personnel. All local safety regulations must of
course be followed including IEE wiring regulations 17th edition if installation is in the UK. The power
supply to the relay is taken from the phase – phase 50 or 60hz voltage and connected via a fuse 6A max to
Um1 and Um2. The CXPLUS accepts any voltage across Um1-Um2 in the range 90-550V 50/60Hz. Voltage
Transformers for different supply voltages are a thing of the past. Check that the supply voltage is within the
limits of the relay rated voltage, and the CT has 1A or 5A output, at full load.
1.2 Current Transformer
The current supply to the relay is taken from a current transformer, which can be split core or ring type
Class 1., with 5VA rating. The current transformer (CT) must be kept short circuited until connections have
been securely applied to terminals K-L. The CT is normally mounted on a different phase to L2-L3 for the
voltage supply. Other connections are possible – see phase offset menu 206. It is essential to ensure:
a)
That the CT is measuring the
total load of the feeder to be corrected – including the PFC capacitor
current
b) The ratio of the CT is such that full load current is about 75% of the CT ratio e.g. for a Max load of
500 amps, select a CT ratio of 800/5 – not 5000/5. This is because at the lower current ranges C T's
are less accurate.
c) Do not use a CT with too low a ratio for the measured load. e.g. If the load is 750
Amps, and you use a 500/5 CT ., the CT will then be saturated and will give inaccurate results.
When mounting the CT, ‘P’ should be pointing in the direction of the incoming supply and ‘L’ towards the
load. S1 on the CT should be connected to ‘K’ on the relay and S2 to ‘L’ on the relay. The output from the CT
can be 1A or 5A. The Max ratio of the CT must be such that the smallest step of switched capacitance will
produce a current of not less than 15mA. Reactive – preferably 20mA.
Example:
The smallest step size is 25 kvar., at 415v 3ph 50 Hz. What is the highest CT ratio permissible?.
25 kvar at 415v = 34.7 amps. Capacitor will switch at 60% of nominal kvar = 20.8 amps.
Minimum current = 20mA reactive ., so Max CT ratio = 20.8/.02=1040/1 or 5200/5 for a 25 kvar capacitor
operating at 415v/3ph/50 hz. A 5000/5 would normally be selected as a max ratio
1.3 Connect the earth tag link
on the instrument case to earth
1.4 Connect in accordance with the wiring diagram
for contactors or thyristors
1.5 Remove any short circuit links from the CT and relay
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