The Right Way to Do Capacitor Bank Installation And Programming

Power factor correction is a key strategy for optimizing energy efficiency and reducing costs. A central component of this strategy is the capacitor bank. 

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But what is a capacitor bank, and why is its installation so critical? In this episode of  Power Grid Podcast, we explore the intricacies of capacitor bank installation, ensuring you achieve a seamless and successful power factor correction installation.

Capacitor Bank Installation: Essential Considerations

A successful capacitor bank installation begins with careful planning and consideration of several key factors.  

Getting these right can mean the difference between an efficient electrical system and one plagued by problems.

Where to Install Your Capacitor Bank

Deciding where to place your capacitor bank depends on a variety of factors, including:

• Indoor vs. Outdoor: Capacitor banks can be installed indoors or outdoors. Indoor installations typically offer protection from the elements but require adequate space and ventilation. Outdoor installations may be exposed to harsh weather conditions, requiring specialized enclosures and considerations for temperature fluctuations.

• Electrical Tie-In: The location of your capacitor bank will determine how it connects to your electrical system. Common options include a parallel connection to existing electrical gear or a direct connection to the secondary side of a utility transformer.

Clearance Requirements

Safety is paramount. Ensure your chosen location adheres to the necessary clearance requirements to prevent electrical hazards and ensure proper ventilation.

Wiring and Breakers: The Backbone of Your Capacitor Bank

Correct wiring and overcurrent protection are vital for the safety and functionality of your capacitor bank.

The National Electrical Code (NEC) mandates that capacitor banks be protected by appropriately sized breakers or fuses. These protective devices should be rated at 135% of the capacitor bank’s rated current.

Standalone vs. Integrated Breakers

You have the option of using a standalone breaker to feed the capacitor bank or choosing a capacitor bank model with an integrated breaker for a more streamlined installation.

Additionally, accurate phasing is essential for ensuring the capacitor bank operates correctly and contributes to power factor correction. Verifying proper phasing before energizing the system is a crucial step.

High Voltage Capacitor Bank Installation

High-voltage capacitor bank installations demand an extra layer of caution and expertise.

Working with high voltages requires strict adherence to safety protocols. Only qualified personnel with experience in high-voltage systems should handle these installations.

High-voltage capacitor banks often require specialized tools and equipment for safe and proper installation. Ensure you have the necessary resources before starting the project.

Programming and Commissioning Your Capacitor Bank

With the physical installation complete, it’s time to focus on the brains of the operation: programming and commissioning your capacitor bank.  This step is crucial for ensuring that your power factor correction installation works as intended.

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Current Transformers (CTs): The Eyes and Ears of Your Capacitor Bank

CTs play a vital role in measuring the current flowing through your electrical system.  This information is used by the capacitor bank controller to determine when and how much capacitive reactive power to inject for optimal power factor correction.

• Placement and Sizing: CTs must be placed upstream of the capacitor bank to accurately measure the current that the capacitor bank needs to correct. Incorrect placement downstream can lead to inaccurate readings and poor power factor correction. Additionally, CTs must be sized correctly to match the current levels of your system.
• Taps and Ratios: CTs have multiple taps that allow you to select the appropriate current range for your system. The correct tap setting, combined with the proper CT ratio programmed into the controller, ensures accurate current measurements and precise power factor correction.
• Controller Programming: Fine-Tuning Your Power Factor Correction
• The capacitor bank controller is the brains of the operation, using the information from the CTs to make real-time adjustments to the capacitor bank’s output.  Proper programming is essential for achieving your desired power factor correction goals.

• Password and Settings: Most capacitor bank controllers require a password for access. You’ll need to adjust the factory default settings to match your specific system configuration, including voltage levels, CT ratios, and other parameters.
• Target Power Factor: The target power factor is the desired power factor you want your system to achieve. This value is typically programmed into the controller and can be adjusted based on your specific energy efficiency goals.

Commissioning Checklist: The Final Steps to Success

Before energizing your capacitor bank, it’s crucial to follow a commissioning checklist to ensure everything is in order.

• Phasing Verification: Double-check the phasing of all connections to ensure they are correct. Incorrect phasing can lead to equipment damage and malfunction.
• Breaker Settings: Verify that the breaker or fuse protecting the capacitor bank is set correctly and will not trip unnecessarily.
• Functional Tests: Conduct a series of tests to confirm that the capacitor bank is operating as expected. This includes monitoring the power factor, verifying that the controller is responding to changes in current, and checking for any alarms or warning signals.

Common Capacitor Bank Installation Mistakes (and How to Avoid Them)

Even with the best intentions, mistakes can happen during capacitor bank installation. Being aware of common pitfalls can help you avoid costly errors.

As mentioned earlier, placing CTs downstream of the capacitor bank is a common mistake that can lead to inaccurate readings and ineffective power factor correction.

Using the wrong CT taps or programming incorrect ratios into the controller can result in inaccurate current measurements and suboptimal performance.

Failing to verify phasing before energizing the capacitor bank can lead to serious consequences, including equipment damage and potential safety hazards.

Overlooking Connections

Loose or poorly made connections can cause problems ranging from intermittent operation to complete failure of the capacitor bank. Always double-check all connections and ensure they are tightened to the correct torque specifications.

Partnering with Power Protection Products for Expert Capacitor Bank Installation

Installing and commissioning a capacitor bank is a complex process that requires specialized knowledge and experience.  Partnering with a trusted expert like Power Protection Products (P3) can ensure that your installation is done right the first time.

P3’s Expertise:

P3 boasts a team of experienced engineers and technicians with a deep understanding of power factor correction and capacitor bank installation.  They have completed numerous projects across various industries, from small commercial buildings to large industrial facilities.

P3 offers a full range of services to support your power factor correction project.  

• Site Assessment and Design: P3 will assess your facility’s electrical system, analyze your power factor, and design a customized capacitor bank solution to meet your specific needs.
• Installation and Commissioning: P3’s expert technicians will handle the entire installation process, from mounting and wiring the capacitor bank to programming the controller and conducting thorough testing.
• Ongoing Maintenance: P3 offers ongoing maintenance and support to ensure your capacitor bank continues to operate at peak efficiency, helping you maximize your energy savings.

Our team will take the time to understand your unique challenges and goals, tailoring their solutions to meet your specific requirements and budget.  With P3 as your partner, you can trust that your power factor correction project is in good hands.

Correct Capacitor Bank Installation 

Capacitor bank installation is a critical step in achieving optimal power factor correction.  By understanding the key considerations, avoiding common mistakes, and partnering with experts like Power Protection Products, you can ensure a successful installation that delivers significant energy savings and improves the overall performance of your electrical system.

Ready to take the next step?  Contact Power Protection Products today to learn how we can help you achieve your power factor correction goals.

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I have a question about a low voltage PowerPack J frame CB that will be used to protect a PF correction CAP Bank.

I was instructed to find the "capacitor interrupting rating" for this CB. So I'm thinking... what the heck is the capacitor interrupting rating of a CB? I was told (briefly) a CB has trouble detecting an abnormal condition and also extinguishing the arc when the PF is 0.

For me, when current is flowing, the CB will be able to detect an abnormal condition by the:
a) Thermal effects caused from electron flow
b) magnetic effects caused by the change of electron flow

How does the PF effect this? What about arcing current, how can arcing becoming problematic when the current leads or laggs the voltage by 90?

What about if current was being detecting via a CT and relay, would the PF then become an issue?

Finally, negleting the issues of a capacitor high energizing currents, short circuit rating and continuous rating, what is also required for consideration when sizing a CB for protecting a PF cap bank?
Ah I see what you mean, so this is an issue of transient due to the interaction with the capacitive bank and the system's reactance from a restrike..
Thanks for the help.

However, what I'm trying to visualize is the CB's max capacitor interrupting rating. How is setting a limit on the current flowing through the protection device reducing the chance of a restrike?
The ability of an interrupter to interrupt current
without restriking is determined by its contact material,
contact design, and gap dielectric field strength. IE: arching is a voltage issue over contact area, not current.

B) How does PF come into play with all of this?

I'm sure that this isn't a completely technically correct response, but this is how I think about the issue for it to make sense:

The interrupting ability is dependent on both current and the transient voltage. Clearly, a breaker would have no problem interrupting a circuit where the load was switched off at the next device. The current interrupted would be very small, but almost totally capacitive, the capacitance of the cable.

The transient voltage across the contacts is related to the power factor. The current is interrupted at a current zero point. With 100% power factor, the voltage is also zero at that point. With 0% power factor, the voltage is at a maximum.
Thanks guys for pointing me into the right direction. I found a very good read here:

Refer to 5.1 Restrike on Page 2 which talks about how the current and voltage angle affects restriking.

The pdf refered me to "IEEE Guide for the Protection of Shunt Capacitor Banks" IEEE Std C37.99-

IEEE Guide said: An important consideration involving application of circuit breakers or circuit switchers for capacitor
switching is the transient overvoltage that may be generated by restrikes during the opening operation. At
current zero, the capacitor is left charged to nearly full-peak line voltage. Little recovery voltage appears
across the switching device contacts at this instant, and the capacitance-current arc is usually interrupted at
the first current zero after the switching device contacts open. After interruption, the normal frequency alternation
of the voltage on the source side of the switching device results in a recovery voltage across the open
contacts, 0.5 cycle later, approaching twice the peak line voltage [see Figure 45(a)]. If a breakdown were to
occur at 90° in Figure 45(b), the capacitor voltage immediately attempts to equalize with the system voltage.
The circuit is oscillatory. At the first peak of the transient, the capacitor voltage will, depending on damping,
overshoot by an amount approaching the difference between the two voltages immediately prior to the
restrike. This high transient overvoltage may damage equipment. If the current is interrupted at the first highfrequency current zero, the transient voltage peak is trapped on the capacitor bank. The recovery voltage
reaches a value greater than that following the first interruption. However, the contacts have moved farther
apart, and the buildup of dielectric strength may prevent additional restrikes.

Thanks for helping me understand about the restrike problem with CB's and Cap Banks. My last question is my original... what is the Capacitor interuption Current Rating of a CB and how does it tie into all of this. Morning jghrist, the reason I ask is because I am getting curious. I want to know the reason why it is necessary to have two ratings for a cap bank load. What's the reason for having what seems to be "a derated CB." As in mentioned case:

1) Continuous Current = A
2) Current Interrupting Duty = 370 A rms

I'm reviewing the IEEE Guide for the Protection of Shunt Capacitor Banks IEEE Std C37.99- to see if I can find an answer or at least clues.
Thanks guys for the input, but it's not what I'm "exactly" looking for.

I'm looking for the reason why the CB continous rating has to be derated for use in Cap Banks. Probably because of the 0 pf and the potential re-striking issue, but why is the current being derated? How does reducing the amount of current flowing through a CB reduce re-stricking? My guess is that by de-rating the CB for Capacitor bank application, you are essentially choosing a bigger CB for switching duty. Hence the CB's contact point would have more surface area thus reducing the chance of arching since it is a function of voltage over contact area.

However, that is my guess... something I came up with. Is it right or wrong? I am looking for the answer.
I read IEEE Std C37.99-00, now I shall read C37.06. Breaker ratings (like fuses, switches and other overcurrent stuff) are designed at a specified (either by the mfg. or by standards) X/R ratio. Capacitor bank X/R approaches infinity. So, what the breaker manufacturer is trying to tell you is even though you have a amp breaker which can be used to switch loads on and off up to amps the switching duty is at the specified maximum X/R ratio, when considering loads having a higher X/R than the standards under which the circuit breaker were manufactured and tested to causes a derating of the device. Switches have the same limitation, you can have a amp gang-operated switch with arcing horns which the mfg. will tell you can break the magnetizing current on a transformer up to some (relatively small) value of transformer MVA (5% of the load rating for example). This is also a reflection of the load break rating based on an X/R ratio which is greater than the standard requirements. S&C's 600 amp alduti-rupter distribution load-break switch is only rated for switching 600kVAr at 15kV (~20 amps) but 600 amps at the rated X/R or less.

Load-break is different than fault-break as the internal mechanisms are different. A piece of equipment has a fault interrupting rating (also stated at a maximum X/R ratio) and a close & latch rating which are different but it's the same device and the same current carrying contacts.

Does this address your question? Hi Apowerengr, Thanks for the input!

I understand what you mean, but as you mentioned: "the magnetizing current." The X/R ratio that we speak of, isn't that the ratio of inductive impedance/resistance?

It is simple to visualize the difficulty when interupting the current of an inductive load due to the fact that I=di/dt can not instantaneously change. As the X/R becomes largers and larger, that is why you are required to derate the CB.

But for a CB that shall be applied for a capacitor bank, I don't see how current will be an issue because the flow can instantly stop (assuming L of the system ~ 0)
That's where my question lies: why for a CB must the capacitor's current be derated?

Note: Another thing, I was talking to Schneider this morning, and they said the LV CB's used for Capacitor bank application have no issues in regards to this (which is great, as my application is for 600V).

It is only when MV and HV CB are used, that you it becomes more application specific where specific duty CB are required for Capacitor Banks. IEEE C36.07- address various CB continous ratings and their dereated current ratings used for Capacitor Bank. Allen Greenwood's Book on Electrical Transients In Power Systems is awesome and I did read this afternoon the section 5.3 on Capacitor Switching as well as Section 6.4 on three phase capacitor switching. It has an excellent explanation on Oscillation, restriking and how shoot through can significantly increase the voltage on a cap.

It explains the cause and derives equation to use for calculations. But it didn't explain why a HV CB would require specific duty ratings and a LV CB does not. Nor could I find an explain why derating a CB's continuous current would solve these problems.

Maybe I'll have to wait until I am at some sort of circuit breaker presentation and ask an expert. This is the text from IEEE C37.012 concerning switching capacitors:-
4.7.1 Capacitor Bank Current.
Circuit breakers are to be applied according to the actual capacitance current they are required to interrupt. The rating
should be selected to include the following effects.
1) Voltage Factor. The nameplate reactive power rating of the capacitor bank, in kilovars, is to be multiplied by
the ratio of the maximum service voltage to the capacitor bank nameplate voltage when calculating the
capacitance current at the applied voltage. This factor can be as large as 1.1, since capacitors can be operated
continuously up to 10 percent above the capacitor rated voltage.
2) Capacitor Tolerance. The manufacturing tolerance in capacitance is -0 to +15 percent with a more frequent
average of -0 to +5 percent. A multiplier in the range of 1.05 to 1.15 should be used to adjust the nominal
current to the value allowed by tolerance in capacitance.
3) Harmonic Component. Capacitor banks provide a low-impedance path for the flow of harmonic currents.
When capacitor banks are ungrounded, no path is provided for zero-sequence harmonics (third, sixth, ninth,
etc), and the multiplier for harmonic currents is less. A multiplier of 1.1 is generally used for a grounded
neutral bank and 1.05 for an ungrounded neutral.
In the absence of specific information on multipliers for the above factors, it will usually be conservative to use a total
multiplier of 1.25 times the nominal capacitor current at rated capacitor voltage for ungrounded neutral operation and
1.35 times the nominal current for grounded neutral operation.

See also the attached Cahier Technique from Schneider.These are available on Schneiders website, but you have to register so I've attached the pdf.

Regards
Marmite  http://files.engineering.com/getfile.aspx?folder=d16bc007-74bf-441f-a18e-efca352afdba&file=ect142(Ctrl_Equip_Caps).pdf