VMtec, Germany

VMtec Maschinen-und
Anlagenbau GmbH
Wiesbaden Hilda str 22
65189 Wiesbaden, Hilda str 22, Deutschland
E-Mail: info@vmtec.de


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POWER FACTOR CORRECTION: QUALITY AND SAFETY

BASIC REQUIREMENT

We define “safety” as the absence of risks for people and equipment when in operation or in a warehouse. This involves the identification of all possible risks; eliminating or controlling them in order to reduce the risk factor to an acceptable level.
The capacitors and the banks MUST NOT to be uses other than power factor correction. If the capacitors are employed for other purposes other than power factor correction even filter components, their use with regard to safety conditions MUST be agreed with VMtec.

GENERAL REQUIREMENT

The capacitors are constructed in accordance with IEC – CEI EN methods, parameters and tests. The low voltage capacitors are assembled with the required protection devices and assembled into banks to give a QUALITY product which will operate SAFELY. They are not considered as the indication that the capacitors and the power factor correction equipment are suitable for a use in the same conditions of the tests.
The user has to verify that the capacitor and power factor correction equipment are the correct voltage and frequency suitable for values of the network on which are installed.
The user has to verify that the installation of the capacitors and/or the power factor correction equipment is in accordance with the catalogue and the instructions of utilization.
Capacitors and power factor correction equipment MUST NOT be exposed to damaging action of chemical substance or to attacks of flora and/or fauna. Capacitors and power factor correction equipments must be protected against risks of mechanical damaging to which could be exposed during normal working conditions or during the installation.
Capacitors and power factor correction equipments that were mechanically or electrically damaged for any reason during the transport, the storage or the installation must not be used and ones that breakdown during use must be immediately removed.

ADDITIONAL INSTRUCTION ABOUT THE POWER FACTOR CORRECTION EQUIPMENTS

Definition

Power factor correction equipment means:
- one or more groups of capacitors that can be connected and disconnected on the network automatically or by hand using suitable operating devices (contactors, circuit breakers, load-break switch, ...);
- operating devices;
- control, protection and measure systems;
- connections.
The equipment could be open or closed inside a metal enclosure.

General requirement

Follow VMtec instructions in the documentation attached considering the safe distance, the connection standard criteria, working standards and the instructions for the controls and the maintenance.

Compatibility

You must pay attention to the electromagnetic interferences with the near by equipment.

Contactors

Contactors used must be suitable for use with capacitors (use category AC6-b) because, having pre-insertion resistance, are able to limit over currents that exist when we connect a capacitor bank

The advance insertion, in respect of the main contactor eliminates the following hazards :
- Stops main contacts WELDING together.
- Avoids capacitor damage.

RECOMMENDATIONS FOR THE INSTALLATION

Fixing and connection

To fix the power factor correction equipments we advise using these types of screws:

  • Riphaso series with M10 screw;
  • MICROmatic and MICROfix series wall-mounted with FISHER 8;
  • MINImatic wall-mounted and floor-mounted with M8 screw;
  • MULTImatic and MULTImatic HLP floor-mounted with M12 screw.

The installation of the power factor correction equipment is for indoor application; for different installations call VMtec technical department.

Protection devices

Operating devices (load-break switch) or operation and protection (circuit-breakers if the cables are longer than 3m) must be dimensioned to withstand capacitive currents (about 1.3 times nominal current), the inrush currents, the number of operations and they must be free from phenomena of re-strike free.
The capacitors are made of polypropylene that is a flammable material. Even if a fire doesn’t begin from the capacitors or inside the panel, they could however spread it creating dangerous gasses. If a danger exists from the presence of an explosive or flammable atmosphere, we have to follow the IEC standard; ”Electric equipment with explosion and fire danger”.

Danger for people

When we install power factor correction equipment we must pay attention that the parts which could be exposed to voltage are correctly protected from accidental contacts in accordance with IEC standards. Before the commissioning verify if the tightening of the terminal and of all the bolts is correct.

PROTECTIONS

Fuses

All the capacitors have an overpressure device which when operated, as in the case of breakdown, disconnects the element from use. It is not a substitution for the fuses or external circuit-breakers that are specified in our power factor correction equipment.

LIMIT CONDITIONS

The influence of each factor below has not to be considered individually, but in combination and with the influence of other factors.

Voltage

Nominal voltage of a capacitor and of power factor correction equipment is the r.m.s. value of the alternating voltage for which the capacitor has been designed. Capacitor units shall be suitable for operation at voltage levels according to table below:

The life expectancy of capacitors and power factor correction equipment is greatly reduced when operating in overload conditions.
The choice of the nominal voltage is determined by the following considerations:
- On some networks working voltage could be very different from nominal voltage;
- Power factor correction equipment in parallel could cause an increase of the voltage at the connection point;
- The voltage increases with the presence of harmonics on the network and/or cosϕ of in advance;
- The voltage at the capacitor terminals increases when capacitors are in series with inductors for the harmonic control;
- If the power factor correction equipment is connected to a motor and not sized correctly, when we disconnect it from the network we may have a phenomena caused by the inertia that makes the motor to work as a self-excited generator consequently increasing of the voltage level at the terminals of the equipment;
- The remaining voltage caused by the self-excited after that the equipment has been disconnected from the network is dangerous for the generators;
- If the power factor correction equipment is connected to a motor with a tardelta starting device we have to pay attention to not cause the overvoltage when this device is working;
- All the power factor correction equipments exposed to overvoltage caused by atmospheric discharge must be protected in correct way. If used the dischargers for overvoltages have to be placed as near as possible to the equipment.

Working temperature

Working temperature of power factor correction equipment is a fundamental parameter for safe operation. As a consequence it is very important that heat generated is dissipated correctly and that the ventilation is such that the heat losses in the capacitors do not exceed the ambient temperature limits. We have the higher working temperature in normal service conditions between two capacitors; we measure at a point 2/3 of the capacitors height and at a distance of 0.1m from them. The capacitors temperature must not exceed the temperature limits hereinafter tabled.

Mechanical Limits

The user has not to expose the equipment to exaggerated mechanical limits of operation. The user has to pay attention to the electrical and geometrical dimensioning of the connections to avoid exceeding the mechanical limits which may be reached by temperature variation.

OTHER CONSIDERATIONS FOR THE WORKING SAFETY

Discharge device

Every capacitor must have a discharge device that can discharge it within 3 minutes. The discharge time is calculated from the starting peak of voltage equal to

Between the capacitor and the discharge system there shall not be a circuit-breaker, fuses or other sectioning devices. This doesn’t relief you to short-circuit the capacitor terminals and earth every time you want handle the capacitor.

Residual voltage

The residual voltage of a capacitor in service must not exceed 10% of the nominal voltage. This condition is generally satisfied in power factor correction equipment by setting reconnection time of the bank at 30 seconds, on the reactive power regulator or adding a further discharging system Between the capacitor and the discharge system there shall not be a circuit-breaker, fuses or other sectioning devices. This doesn’t relief you to short-circuit the capacitor terminals and earth every time you want handle the capacitor.

Case connection

The cases of all metallic capacitors are fixed at Earth. The case is earthed to the frame on which the capacitors are fixed.

Altitude

Power factor correction equipment must not be used above an altitude of 2000m. On the contrary please contact technical assistance of VMtec.

Particular ambient conditions

Power factor correction equipment are not suitable for the applications in places
where there are conditions as follows:
- Fast generation of mould;
- Caustic and saline atmosphere;
- Presence of explosive materials or very flammable;
- Vibrations.
For environments with these characteristics: high relative humidity, high concentration of dust and atmospheric pollution, please contact technical assistance of VMtec.

MAINTENANCE

After the disconnection of the bank, prior to accessing the terminals of the capacitors wait 5 minutes and then short-circuit the terminals and earth.
Make these procedures:
Once a month
- Cleanliness by blast of air of the internal part of the power factor correction equipment and of the air filter anytime there is a cooling system;
- Visual control;
- Control of the ambient temperature.
Once every 6 months
- Control of the surfaces condition: painting or other treatments;
- Control of the correct tightening of the screw (this operation must be done before the commissioning).
If there are concerns about any environmental conditions an appropriate maintenance program must be established (for example: In a dusty environment could be necessary to clean using blasts of air more frequently).

STORAGE AND HANDLING

Handling of the power factor correction equipment must be done with care avoiding mechanical stresses. Capacitors not installed must be stored with their packages in a dry and protected place.