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Frequently Asked Questions on Power Factor Controls and Correction
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The FAQs on our power factor controls and power factor correction are organized into technical and administrative (order processing, shipping etc) sections.


TECHNICAL FAQ

General, all products
1. What is power factor and why is it important?
2. What are the considerations in selecting the capacitor bank switch?
3. What are the functional differences between your various controls?
4. Which applications are best suited for regulation mode and which for compensation mode?
5. How can PFC systems be protected during line faults?
6. How and when do bypass relays fail?
7. When are harmonic filters needed?
8. How much money do I save?

PFC1 related FAQ
1. Which power factor measurement and correction method does the PFC1 use?
2. How can the PFC1 controlled capacitor banks be sized for a given load?
3. What type of capacitor bank switch can be used with the PFC1?
4. How are PFC1 faults handled?
5. What are the considerations in setting the PFC1 measurement time?
6. Why use the PFC1 initial output setting facility?
7. What is the operating control sequence of the PFC1?
8. Can one set of PFC1 outputs drive the capacitor banks and the other signal a PLC?
9. Why deactivate the PFC1 at currents less than 10 % of range?
10. Which line voltages does the PFC1 cover?
11. Why is the PFC1 not front panel mountable like most other power factor controllers?

RCCSx and RCCx related FAQ
1. Which power factor measurement and correction method do the RCCSx and RCCx use?
2. How can the RCCSx and RCCx controlled capacitor banks be sized for a given load?
3. What type of capacitor bank switch can be used with the RCCx?
4. What are the considerations in setting the RCCSx sampling time?
5. What is the operating control sequence of the RCCSx and RCCx?
6. Which line voltages do the RCCSx and RCCx cover?

PFCD related FAQ
1. How can a PFCD be used to measure power factor?

 

ADMINISTARTIVE FAQ
1. Can I buy samples for immediate delivery?
2. Can I buy ex-works (I have my own courier/agent)?
3. Is there a minimum order quantity?
4. I would like to promote/market/distribute this technology in my area. What do I do?


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TECHNICAL FAQ

General, all products

1. What is power factor and why is it important?

Power factor is the ratio of active power (measured in W) to apparent power (measured in VA) in a line and is a measure of the current capacity utilization of the distribution circuits (the higher the better). With linear loads and sinusoidal voltage and current waveforms the power factor equals to the cosine of the phase angle between the current and voltage vectors. All practical loads employ a magnetic circuit (motors, transformers etc) which introduces inductance in the circuit and results in out-of-phase voltage and current vectors. The inductive current circulates without producing useful work between the source and the load and effectively reduces the distribution network capacity (limited by the wiring cross-section area). In addition, the higher current results in higher conduction losses and may falsely trip protective devices.

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2. What are the considerations in selecting the capacitor bank switch?

Solid state relays (SSRs) must be of the synchronized (or zero-crossing) type and use a suitably dimensioned heatsink. The zero-crossing property ensures that the capacitors are switched in when the line voltage equals the capacitor voltage thus eliminating capacitor inrush current, the generation of harmonic currents/ringing and extending capacitor life. The capacitor discharging resistors are for safety reasons only and can be any suitable value giving minimum heat dissipation while the bank is connected to the line. The SSR conduction losses can be minimized by employing a suitably timed bypass relay.

Contactors must be of the special two stage design limiting capacitor inrush current at bank switch-in. The capacitor discharge resistors must be sized to optimally bring down the capacitor voltage (using the PFC1 or VSPFC capacitor time-out/discharge protection feature) before a possible switch-in to minimize the average inrush current and keep heat dissipation at acceptable levels. Also, as contactors are slow devices they cannot be driven at fast sampling times. Furthermore, as the finite inrush current contains/generates harmonics, series detuning chokes may have to be used to protect the capacitors (see this FAQ below).

Our CACSW integrated PF capacitor AC switch combines the advantages of bypassed SSR switching and phase fault detection to monitor line status and fuse state.

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3. What are the functional differences between your various controls?

Our controllers operate under two power factor correction modes: regulation or compensation. In regulation mode the current is detected at the line side of the capacitor connections and equals to the sum of the load and connected capacitor currents. In this mode the controller must switch capacitor banks in and out of the line to minimize reactive current at the line side. In compensation mode the current is detected at the load side of the capacitor connections and is equal only to the load current. In this mode the controller switches the banks in and out of the line to compensate the detected reactive load current as closely as feasible by the available bank sizes.

The PFC1 and AVSR3 control in regulation mode measuring the resulting power factor after switching compensating capacitors in and out of the line to maximize it. The detecting current transformer is placed on the line side of the capacitor connections.

The RCCSx and RCCx compensate the detected reactive load current after a set value by fixed amounts. The current transformer monitors the load current only and so it is placed on the load side of the unit.

The VSPFC can be set to operate in regulation or compensation mode.

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4. Which applications are best suited for regulation mode and which for compensation mode?

This is more a question of product correction method focus and installation practicalities than the advantages/disadvantages of each mode.

The PFC1 and AVSR3 focus on the resulting PF (or reactive current) and so operate in regulation mode. The RCCSx and RCCx switch capacitors at preset levels of reactive load current and so are compensation mode. The VSPFC operates under any of the two.

Installation practicalities to address include the feasibility of physically placing the detecting current transformer at the line or load side (usually not an issue) and running the connecting cables to the capacitor switches and banks.

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5. How can PFC systems be protected during line faults?

During a line fault bank switches can disconnect and/or reconnect the capacitor bank uncontrollably and as a result capacitor charge will flow as DC through any available path. With a failing line, protection electronics may not work properly and fuses may blow as disturbance currents flow.

Contactor switches may reclose (or "chatter") while in the full contact position for a few milliseconds causing large inrush currents and conducting SSRs will not turn off until the capacitor current has completely died off. One particularly nasty combination of events is when two conducting SSRs form a voltage doubler with their associated capacitors stressing components beyond design values.

In cases where the load is always connected to the PFC system, the capacitors can discharge with minimum problems through the low DC ohmic value of the load (e.g. a few ohms for a motor). The same applies when other loads are connected on the line side of the system. As such a PFC system is most vulnerable when it is on its own with trapped conducting capacitor charge flowing through the system parts.

To protect against such contingencies, the following actions may be considered:

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6. How and when do bypass relays fail?

Bypass relays are used to short their associated solid state switch when already on to eliminate their conduction losses. As such they close and open across a low voltage (well under 2 V) and so are not electrically strained. They are however mechanically fatiqued and will eventually fail following a number of operations. Typical figures for this is x100 times the rated relay contact operations, for example the typical relay designed for 100000 full load switching operations will perform at least ten million no load operations. As a result the service life of the relay is a function of the employed sampling time (the longer, the better) with the absolute worst case service life being equal to sampling time times twice the mechanical operations limit. As an example, with a 5 s sampling time, this worst case calculation gives a service life of three years.

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7. When are harmonic filters needed?

Harmonic filters take the form of series chokes with each capacitor and are needed when harmonics are present in the line. Harmonics cause proportionally higher currents to flow through the capacitors and as a result stress them and reduce their operating life. Their cause can be any non-linear load (such as any equipment with a line-side rectifying stage) or the capacitors themselves if switched/connected uncontrollably (such as by a contactor or electromechanical switch, see this FAQ).

As such, harmonic, detuning filters are needed in the presence of high harmonic distortion and/or when contactors are used to switch/connect the capacitors to the line.

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8. How much money do I save?

It depends on the applicable tariff. Clearly, when the power factor, reactive power or excess demand is measured and involved in the bill calculation, the savings are considerable and in direct proportion to the effectiveness of the employed power factor correction technology.

In the case of active power only tariffs, the savings reflect the reduced wiring and other conduction losses and, depending on the type of installation and load profile, can be typically anything from 1% to 7%.

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PFC1 related FAQ


1. Which power factor measurement and correction method does the PFC1 use?

The PFC1 measures the phase angle between the load current and voltage vectors and corrects the measured inductive power factor by switching in and out of the line compensating capacitor banks.

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2. How can the PFC1 controlled capacitor bank be sized for a given load?

A simple and practical method is to provide the load active power in capacitor reactive power (KVArs) in three steps. As an example, a 15 kW load can be compensated with three 5 kVAr capacitor banks up to a worst case power factor of 0.7.

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3. What type of capacitor bank switch can be used with the PFC1?

Solid state relays (SSRs) and any mechanical switch such as contactor relays.

The CACSW integrated PF capacitor AC switch is a particularly "elegant" solution for up to 3x25 A.

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4. How are PFC1 faults handled?

During a fault the PFC1 outputs are deactivated and the error condition clears automatically after its cause has been removed.

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5. What are the considerations in setting the PFC1 measurement time?

The PFC1 measurement averaging and sampling time can be set to 1, 3, 5 and 15 seconds in models with external control input or 1, 2, 3 and 5 seconds in older models without this input. Choosing this time depends on the monitored load dynamics and the required response time.

The choice of bank switch type is also important as switching mechanical relays at high rates affects their reliability and service life. Solid state relays (SSRs) are not affected by the choice of measurement time.

The CACSW integrated PF capacitor AC switch has a maximum response time of 2.5 seconds and as such can be switched at the 5 s or 15 s rate.

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6. Why use the PFC1 initial output setting facility?

The facility is useful for compensating loads approximately while the first measurement is being performed. This allows for "kickstarting" load compensation to a given level and so converge faster to the high power factor state (better than 0.95).

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7. What is the operating control sequence of the PFC1?

On activation (current higher than 10 % of range) the outputs are initialized as set by the DIP switch until the first measurement is completed. From then on and at every new measurement the outputs remain unchanged until the next measurement is complete if the measured power factor is above 0.95. The outputs are incremented (the next step is activated) for inductive power factors below 0.95 and the output protection time-out has elapsed. Correspondingly the outputs are decremented (the highest step is deactivated) for capacitive power factors below 0.95.

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8. Can one set of PFC1 outputs drive the capacitor banks and the other signal a PLC?

Yes. The 24 VDC and contact outputs are galvanically isolated from each other and can be used in different circuits.

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9. Why deactivate the PFC1 at currents less than 10 % of range?

Compensating small loads may cause more problems than is worth. In the typical case the first step capacitor will overcompensate and the system will toggle between capacitive power factor (capacitor in) and inductive power factor (capacitor out) with the capacitive current being a lot higher than the load current (the one to be corrected).

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10. Which line voltages does the PFC1 cover?

Currently the PFC1 is available for the following standard European and US lines: 1x110-120 VAC, 1x220-240 VAC, 3x120 VAC, 3x240 VAC, 3x400 VAC and 3x480 VAC. Please contact us for other voltages.

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11. Why is the PFC1 not front panel mountable like most other power factor controllers?

The PFC1 is designed for simple (up to three step), low-end applications such as power factor compensation for a domestic lift. On the other hand front panel mountable controllers address more demanding applications which require more compensating steps, set-up parameters and monitoring functions.

The PFC1 is designed to be very simple to install (only two parameters to set-up via the DIP switch, no front panel interaction needed) and requires the absolute minimum of external components (the current transformer, the capacitor bank switches and the capacitor banks themselves) to provide fast (1 to 15 seconds process time) power factor compensation for a variable load.

Also, being DIN rail mountable allows it to be enclosed in a high IP rated enclosure for use in adverse environments.

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RCCSx and RCCx related FAQ


1. Which power factor measurement and correction method do the RCCSx and RCCx use?

The RCCSx and RCCx measure the load reactive current and compensate it by switching in and out of the line capacitor banks.

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2. How can the RCCSx and RCCx controlled capacitor bank be sized for a given load?

A simple and practical method is to provide the load active power in capacitor reactive power (KVArs) in the available steps.

As an example, a 15 kW load can be compensated with a RCCS3 with three 5 kVAr capacitor banks up to a worst case power factor of 0.7.

Single step RCCS1 and RCCx capacitor banks are sized to be equal or just less the load they are compensating.

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3. What type of capacitor bank switch can be used with the RCCx?

Solid state relays (SSRs) and any mechanical switch such as contactor relays.

The CACSW integrated PF capacitor AC switch can be used for capacitors up to 3x25 A with its "Ready" output as status feedback.

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4. What are the considerations in setting the RCCSx sampling time?

The RCCSx measurement averaging and sampling time can be set to 4, 8, 16 and 32 seconds. Choosing a suitable time depends on the monitored load dynamics and the required response time.

Clearly, a longer time taxes the RCCSx bypass relays less.

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5. What is the operating control sequence of the RCCSx and RCCx?

The RCCSx and RCCx switches are activated when the detected reactive current is above their respective set value as determined at each unit's potentiometer. Switch activation/deactivation happens at every sampling instant as set at the DIP switch (RCCSx only).

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6. Which line voltages do the RCCSx and RCCx cover?

Currently the RCCSx and RCCx are available for the following standard European and US lines: 1x110-120 VAC, 1x220-240 VAC, 3x120 VAC, 3x240 VAC, 3x400 VAC and 3x480 VAC. Please contact us for other voltages.

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PFCD related FAQ


1. How can a PFCD be used to measure power factor?

For this, an active output PFCD (PFCDxA models) is preferably used. The receiving PLC/control can estimate the power factor as the quotient Active current value/Apparent current value. The sign will indicate capacitive or inductive power factor.

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ADMINISTRATIVE FAQ

1. How can I buy samples for immediate delivery?

Online here or by contacting us with your special instructions. We make every effort to have sampling quantities of standard models ex-stock for quick worldwide delivery.

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2. Can I buy ex-works (I have my own courier/agent)?

Yes, by contacting us with your requirements and instructions.

[ Back to FAQ List ]


3. Is there a minimum order quantity?

No, but note that shipping/handling charges become proportionally higher with smaller orders.

[ Back to FAQ List ]


4. I would like to promote/market/distribute this technology in my area. What do I do?

Contact us!

[ Back to FAQ List ]

 


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