Automatic regulated MV capacitor banks ACR, ACRD type
General information:
Automatic regulated capacitor banks ACR/ACRD type are the example of the most modern technical solutions in range of MV power factor correction. They are designed for group or central compensation in industrial networks up to 24kV. Capacitor banks are equipped with microprocessor protection and automatics system.
Symbolics of the type:
| Execution: |
Capacitor units: |
Housing: |
| |
1Y
jsingle-phase, connected in star |
...z |
ACR
without reactors |
2Y
single-phase, connected in double star with unbalance protection CT |
regulation grade in cubicles, capacitors and reactors (if applied) on steel constructions |
ACRD
with resonance reactors |
3
three-phase (ACR only) |
no marking
in cubicles |
First cubicle of the capacitor bank is wider, providing function of cable incomer. On request, capacitor banks might be equipped with separate incoming cable cubicle with load-break swith (above 630A - circuit breaker).
Example of installation: ACRD-2Yz capacitor bank (network voltage 6,3kV, execution with resonance reactors, capacitors in double star, distribution equipment in cubicles, capacitor nad reactors on steel constructions, switched by means of vacuum contactor)
1. Capactitor and reactor constructions:
Capacitors, reactors and unbalance protection CT are assembled on steel construction. The construction is electrostatically powder painted.
Draw. 1. Capacitor-reactor grades
Capacitor-reactor grade consists of:
- power capacitors connected in double star system (minimum 6 capacitor units);
- unbalance protection CT 25/5 A/A;
- three-phase iron-cored reactor, which's phase inductances create with capacitors' capacitances a resonance circuit tuned for resonance frequency fr=189Hz;
- support insulators, including three insulators with capacitive voltage dividers for supply presence monitoring (optical indicators assembled near fence's gate are fed from voltage dividers).
2. Regulation grades:
For each capacitor-reactor grade, there is a regulation grade assembled in steel cubicle IP31 provided. Width of the first grade is wider by 200mm than others, ensuring possibility of supply cables incoming. In this grade, on main bus-bars, surge arresters are provided. In upper part of cubicles there are control compartments. Each grade is fed from bottom or in lower part of rear wall.
Equipment of the regulation grade consists of:
- fused vacuum contactor
- overload protection CT's
- earthing switch
- protective and control automatics
- interlocks system
- surge arresters (in the first grade, common for bus-bars)
3. Automatic control and protection system:
Following protections are applied in the capacitor bank:
- power fuses - against phase-to-phase short-circuits
- surge arresters - overvoltage protection
- integrated microprocessor system
4. Protection against transients (switching overloads and overvoltages)
Automatic regulated capacitor banks are equipped with surge arresters, which protect capacitors and distribution apparatusses against overvoltages, which can take place in the moment of capacitors' disconnection. Surge arresters protect also capacitor bank against external overvoltages, as switching overvltages or atmospheric discharges.
Effective limiting of inrush currents and their periodical component frequency guarantee application of resonance reactors, which's inductances are much higher than required.
5. Service safety:
Service safety is assured by means of:
- grounding as a protection against electric shock
- safe, visible insulation distances realised by putting out of fuse links in regulation grades
- earthing switches in supplying and regulation grades
- interlocks' system
Multiple interlocking system in regulation grades ensures full service safety and exludes possibility of improper switching operations:
- interlock preventing opening of regulation grade's door if the earthing switch in this grade is open
- interlock preventing closing of grade's earthing switch (and therefore opening of grade's door) in time shorter than discharging time of capacitors (counting from contactor's main contacts opening) if earthing switch in supplying grade is open
- interlock preventing closing of grade's earthich switch if circuit-breaker on supply is closed and relative earthing switch is open
- switching off and interlocking of contactor preventing its closing when the earthing switch in the grade is closed or being tried to close
- interlock preventing contactor's switching on if regulation grade's door is open switching off and interlocking of contactor preventing its closing if power fuse is blown or missing
- interlock preventing contactor's switching on if circuit breaker on supply is open
- interlock preventing circuit breaker's switching on if any door of regulation grades is open or any earthing switch is closed
Additionally, service safety is ensured by optical signalling of voltage presence on each capacitor bank's grade (insulators with capacitive voltage dividers). Signalling panels are placed in visible place.
