Pre-commissioning of Electrical systems is an important part of the commissioning process.  If not done properly, small issues can become much bigger issues if not addressed during pre-commissioning. The first thing that takes place prior to pre-commissioning is Mechanical Completion. The handover from the construction team to the commissioning team precedes pre-commissioning, for the commissioning team to then proceed with pre-commissioning activities. that’s done by the commissioning team itself. The systems are installed, mechanical completion takes place, and they are handed over to the commissioning team. The commissioning team then starts to perform electrical pre-commissioning activities. For more details about the commissioning process, read The Commissioning Process: A Step-by-Step Guide

Let’s review some typical electrical pre-commissioning activities.

Vendor Site Acceptance Testing (SAT)

An example of pre-commissioning is Vendor Site Acceptance Testing or vendor SAT. This is very similar to factory acceptance testing with the exception that now testing is done on site. The vendor may have completed a certain set of tests in the factory. They’ll typically come to site and do some of those tests or all of those tests again, on-site once the equipment is installed. This confirms there was no damage during shipping or installation. Similar tests could be performed as were done in the factory. If performance tests were performed on a pump in the factory, the vendor will travel to site to confirm that their equipment is still intact and meets all technical requirements after installation.  The pump curve may be measured again on site to confirm that it still meets technical requirements that were measured in the factory. With these two sets of results from the factory and from onsite testing, the commissioning team can compare FAT and SAT results to see if there’s any differences. The vendor can confirm that they have delivered contract compliant equipment, that the equipment meets all technical requirements, and is therefore available to proceed with further commissioning.

The vendor will then sign off on their equipment confirming that it meets all technical requirements. The vendor, the contractor, the owner, and the commissioning team will sign off, confirming that the  equipment meets specification and can be used for further testing during subsystem and system tests.

Grounding and Bonding Checks

Some  easier pre-commissioning checks are grounding and bonding checks. Before the power is applied to the systems, integrity of the grounding system and bonding system needs to be verified. This is checked before first power is applied, because if there are any issues during energization, this is the system that will direct any hazardous energy to ground and protect the equipment and protect people that are working in the area. Grounding and bonding checks are typically confirmed visually and the resistance of bonds measured to ensure bonding to all metallic surfaces is in place.

Cold Loop Checks and Megger Checks

Prior to mechanical completion, the construction team would (should) have completed point to point checks, or cold loop checks. Point to point checks confirm that all the cables and conductors are terminated to the correct terminal blocks.  Any wiring errors are identified during these checks and rectified prior to cubicles being energized on-site.

As well, megger checks are completed.  Megger checks apply voltage across the cable conductor and insulate to confirm that the cable has not been damaged or punctured to degrade the dielectrics of the cable. When megger checked, cables should produce a very low current between the conductor and insulation.  Cables can be megger tested individually, or tested as a bundle by tying all conductors and shields together prior to termination.  Check your technical specification on the requirements for megger testing, if bundle testing is permitted.

Pre-Energization Checks

Once all the cables have been pulled and terminated, the cubicles can be energized for the first time. One basic thing to check before energization are power polarity checks – to confirm that the cables are installed correctly, that power is not supplied backwards to the cubicle and potentially causing damaging to the equipment, or causing any safety hazards. 

Hot Loop Checks

Following mechanical completion and following energization of the cubicles, hot loop checks or operational loop checks can take place. Loop checks confirm the integrity of a control loop of the system from the HMI to the end device, including all cables and instruments. Hot or operational loop checks confirm the following:

• That cabling from the cubicle is intact
• That field sensing devices are properly installed
• That the field device is properly calibrated
• That the field device can successfully communicate with the HMI system
• That ranges and set points are correct
• And that information is correctly displayed on the HMI.

During these hot loop checks, alarm points are verified by stimulating the field device and confirming that the correct alarms are generated and logged.

Loop checks consist of verifying digital and analog I/O.  Digital discrete logic is verified to confirm that high/low signals are received correctly.  Analog I/O consist of 4 – 20 MA signals received by the PLC and displayed on the HMI, scaled to indicated the measured value.

For discrete digital I/O, signals may need to be triggered in the field during loop checks, since the plant process is not running.  This could include placing a temporary jumper across the terminals of the end-device to simulate an open/closed contact.  If temporary jumpers are applied, be sure to keep track of every point this has been done for.  One of your pre-startup checks will be to verify that these have all been removed.  Your plant process will not work well if any of these are forgotten and remain in place during plant startup.

Let’s use a level sensor in a tank as an example of an analog I/O.  Without the actual plant process started up and running, you may have to stimulate the level sensor to simulate varying levels within the tank. This could be as simple as just a piece of cardboard on a stick, moving it up and down, and allowing the level sensor to measure the different levels of the tank. As you’re doing that, you will see that the corresponding information is showing up on the HMI correctly, that it’s scaled correctly, that you’ve got the current polarity, and that you can read the information correctly on the HMI. The reason you want to do this is because once you actually have process fluids in the tank and everything’s working as a system, you don’t want to find out that the level sensor is not working or is not scaling the 4 – 20 MA signal correctly – it is best to check this during pre-commissioning, to make sure that all the end devices are working before you actually start running the plant as a system.

Loop checks can be performed as open loop checks or closed loop checks:

• Open loop checks confirm that the HMI can correctly control the device, such as turning a pump on
• Closed loop checks control the device, and also receive status of the pump to confirm that it has receied the run command and is actually running.  This can be done by monitoring a run status signal, or measuring the RPM of the motor to confirm it is running at the desireed speed.  This closed loop feedback can be used to adjust the run command to achieve the desirted speed.

AC Phase Checks

Before 3-phase systems are energized, phase checks are completed to verify installation of each electrical phase in the proper order. If 3-phase power is installed backwards, called phase rotation, the system may rotate in the wrong direction, or worse, some equipment can’t tolerate incorrect sequencing of phases, and be potentially damaged or destroyed. For larger power systems, visual verification to confirm that buswork is correct may be required. This confirms that risers are connected correctly from transmission lines to the buswork in an AC station. For smaller power systems, each phase can be measured to confirm that phases are installed correctly. A phase rotation meter can be connected to the equipment before power is terminated to the equipment to confirm the proper phases are connected.

Transformer Checks

Transformer checks are done before and after first energization. Prior to the first energization, oil samples are taken, and these are compared to oil samples that you will take after energization. When you compare the two samples, you will see if there’s any differences between the samples that could indicate an internal problem with the transformer. If you see additional particulates or elements that are part of the second sample, that could be an indication of off-gassing within the transformer due to hotspots or improper bonding.

Winding resistance measurements are taken as well as insulation resistance. These are typically done in the factory, but sometimes for larger units, they may be done at site as well. Results from the factory are compared to the onsite results to confirm that nothing was damaged during shipping.

Transformer ratios are measured once tap changers are set to confirm ratio of primary to secondary windings.

And once the transformer is energized, open circuit test are conducted to measure the no load current losses. As well, short circuit tests are performed with reduced voltage to the primary winding to measure full load current losses.

Protection Relay Testing

Protection relays are used within electrical systems to monitor voltage and current and provide rapid response to safe the system should there be any fault detected. The relays monitor the electrical properties of the systems, primarily through PTs or CTs, to measure voltage and current. The relays sense any anomolies or disturbances of the system and react accordingly, according to the settings that are applied to the relay.

The first step is to verify that the correct settings have been applied to the relay. Your engineering team has likely conducted a protection coordination study, which is coordinating the settings of relays, breakers, trip settings, fault settings, all of the protection settings across the entire system. The protection coordination study determines what each device settings should be. The settings particular to each device are important, and you will want to make sure they are properly applied within the relay before proceeding with further tests.

Each relay communicates with the PLC systems and the HMI, and verification of the values that are returned to those systems is requried. This includes verification that the polarity is correct for each PT and CT. This is something to watch for since I have seen situations where a CT is wired backards. As soon as power is applied for the first time, the unit is going to trip off instantaneously since the relay measures current in the wrong direction. Also confirm that you’re not getting two negatives, a backward CT plus a programming error in the PLC, which is displaying correctly on the HMI. If this is the case, you may be receiving a false reading.

Primary and secondary injections of the CTs and PTs are performed to verify relay inputs. Secondary injections can be applied to prove the operation of the relay at one or more settings values. Primary and secondary injections are used to test the protection scheme logic to ensure that alarm set points are responding correctly, that the system is logging alarms, and tests that the logic is reacting correctly based on the faults that are being triggered.

The commissioning team may require that the supplier or vendor of the equipment perform the relay protection settings, or the owner may have the capabilities to do their own protection relay testing. This is a specialized skill to be learned. If you would like more details on relay protection testing, go to relaytraining.com.

Interlock Verification

Electrical systems are often designed with interlocks to prevent the system from entering an unsafe operating scenario that could damage equipment or cause harm to people working in the area. For example, an electrical system could have two incoming feeds from the utility – two redundant power feeds each feeding one half of a switchgear line up, and the other utility feed powering the other half of a switchgear line up – and these are normally powered independently. But there could also be a tie-breaker between the two switchgear lineups. You would never want to be in an operating scenario where you have both incoming utility feeds closed, as well as the tie breaker. This can destroy the equipment and cause safety concerns that could hurt personnel working in the area.

The system would be designed so that it can never enter this operating scenario. If both of the utility incoming feeds are closed, interlocks are in place that would prevent the tie-breaker from closing. If you tried to close the tie-breaker, the system would physically prevent it from closing. Alternatively, if one of the utility feeds is de-energized, and the secondary power feed remains energized with the tie breaker closed, the other utility breaker won’t be permitted to close until that tie-breaker is opened. Interlocks are a critical safety factor that must be verified before applying first power to any of the equipment. They’re often hardwired rather than relying on automation systems to protect people and equipment. And since they perform such a critical safety function, they must be checked prior to energization.

All interlocks are verified by operating equipment without the bus voltage applied. The equipment is operated in all configurations to confirm interlocks operate as designed. Essentially this is a truth table to verify that if one component is closed and another is closed, then another particular device must be open. All the different configurations in your truth table will be verified to confirm that all interlocks are functioning correctly before applying any power to the system. If you do encounter any issues during your interlock testing, these are rectified before moving on to the next stages of the tests.

Motor Tests

Motors are a common piece of equipment in industrial plants, and they need to be fully tested prior to being placed in service. Initial checks include visual verification of the motor to ensure there is no damage during shipping or installation. A manual rotation of the shaft will confirm that it can freely and smoothly be rotated by hand. Examine the motor name plate and compare the operating and rated values of the equipment. With a multi-meter, verify that the motor is properly bonded and connected to the grounding system. Perform AC phase checks to confirm power cables are correctly terminated to the motor. Measure the motor winding continuity and resistance using a multi-meter and compare to the nameplate values. Measure the phase-to-phase insulation resistance, and phase-to-ground insulation resistance. This is called hi-pot testing, exlained further below.

Once all the checks are complete, the motor can be energized. Initially, it would be uncoupled from the piece of equipment that it’s running. This is called an uncoupled run and this allows measurement of the no load current. The motor can then be coupled to the equipment that it’s running, such as a pump. Repeat the same measurements to measure the current at three different points on the pump curve. This confirms rated operating current and confirms that the motor and the pump coupled together are operating correctly.

AC and DC Hi-Pot Tests

Hi-pot stands for high potential or high voltage. This measures the ability of a dielectric to withstand rated and transient voltages. Hi-pot tests are the opposite of continuity tests and confirm that no current will flow from one point to another. Voltage is applied between ground and the conductor. If the insulation between ground and the conductor is sufficient, the application of a large voltage results in a very small current. The applied voltage and the duration of the applied voltage depend on the local standards and codes in your area – typically double the rated voltage plus 1000 V for one minute.

The voltage applied can be either AC or DC as determined by your technical specification or local codes and standards. This test does work with very high voltages, so it can be a very hazardous test and is typically done by experienced personnel. If you’re involved in this test, it’s very good to get paired with an experienced commissioning engineer who has done these types of tests in the past so that you can learn how to do them safely and properly.

Battery Discharge Tests

Battery bank systems are tested during pre-comissioning to verify they function correctly and can be depended on when needed during a power loss. A battery discharge test will confirm that individual cells and batteries meet the technical requirements of the specification. Your technical specification will specify many hours of rated voltage and current is required. Cells can sometimes be damaged if they’re not stored correctly or if they’re not charged and cycled correctly – you want to verify that the battery system has not already lost half of its in-service life, and verify that the owner is receiving full life of the battery system to last for the years.

There are two tests to complete for battery tests – cycle testing and load testing. Cycle testing subjects the battery bank to multiple charge and discharge cycles to confirm that cells meet the manufacturers life cycle rating. Charge and discharge rates are measured for several cycles, and can be used to estimate the life cycle of the batteries. This shorter period of time can be used to determine how long the batteries will last and if they’ll meet their lifetime requirements.  Load testing verifies that the battery bank can deliver the specified power when required. A static or a dynamic load is applied to the battery bank and it is used to discharge to the specified depth of discharge. This length of time confirms that the battery bank can provide the required power for the required duration of time.

Balance of Plants Systems or Building Commissioning

There are several other auxilliary electrical systems within an industrial plant, and these are referred to as balance of plant systems. These are important systems as they enable the building to support the actual plant process or intended function that the system should perform.  Another term for these systems is building commissioning, and these are the auxilliary electrical systems enabling the building and support systems to function. Examples would be an HVAC system, emergency lighting and control systems, or public announcement system. Each of these systems require pre-commissioning activities, or may be part of a larger system requiring pre-commissioning activities.

While the building commissioning isn’t the primary focus of the commissioning team, it cannot be overlooked.  An HVAC system that is not functioning correctly can trip off the main plant process if temperature limits are not maintained.

Deficiencies During Pre-commissioning

An important aspect to consider is deficiency classification during pre-commissioning. Any deficiencies that are identified during pre-commissioning are added to the deficiency tracking list that was created during factory acceptance testing and either classified as a Type-A, Type-B or Type-C deficiency.

A Type-A deficiency is anything that must be corrected immediately before proceeding any further with commissioning.  A Type-A deficinecy causes a functional problem with the system that must be addressed for further testing to proceed, or causes a safety issue.

A Type-B deficiency is an item that does need to be corrected before hand over to the owner, but doesn’t impact the function or operation of the equipment.  Commissioning can continue while the Type-B deficiency is addressed before handover.

A Type-C deficiency is minor in nature and doesn’t need to be corrected immediately – it can be corrected after hand over to the owner. An example of a Type-C deficiency would be a minor cosmetic finish or paint scratch on the wall or something that’s not necessarily impacting the function or operation of the system.  The deficiency does need to be corrected, but could be corrected at a later date.

Pre-commissioning Completion

Pre-commissioning is complete once you’ve completed all your checklist and verified that each piece of equipment meets the technical requirements of the project. Pre-commissioning tests the equipment as a stand alone item. Tests during pre-commissioning don’t neccessarily operate the euipment as a system yet. Each piece of equipment is confirmed to be ready for further commissioning during the commissioning phase.  Pre-commissioning is also known as vendor startup, since each vendor’s equipment is started for the first time on site to confirm function of each piece of equipment.

The components start to come together as a system during the commissioning phase.  You can learn more about each phase of the commissioning process here.

If you’d like to learn more about the commissioning and startup process, please join our free three-day mini course. The course is free and flexible to take any time online. It gives you a great overview to understand the commissioning and startup process.

The questions and answers below from our live Q&A webinar on electrical pre-commissioning.

Live Webinar Question and Answer 

Some companies and factories who produce machines don’t care about the right safety procedures. What should be done in this situation?

That’s very concerning to hear if safety factors aren’t being considered, that needs to be corrected. If the company that’s providing the equipment is not interested in safety at all, then I would say that’s not a company that anybody could work with (more safety details here: Safety During Commissioning).  You can’t be putting hazards in the workplace that are going to cause issues for operators and owners in the future. As an example, if a piece of equipment is being supplied and the company refuses to put a mechanical guard around a rotating chain or a belt, then you can’t have that type of equipment in the workplace.

That’s just not safe, and you can’t be presenting those hazards to the owner. That’s a question for the owner or the project team, if they’re willing to work with that company and retrofit and install something on site after the fact to make sure that it’s safe.  If additional safety guards need to be applied, then that could be an option, but it’s not a good situation. Hopefully in your procurement specification, those types of safety guards are being specified. And that would be a reason to exclude that vendor if they refuse or cannot meet the safety requirements of the technical specification.  Then proceed to vendor number 2, or vendor number 3 that can meet the safety requirement.

Can you tell us what kind of measuring equipment we should use for the test? The good ones. 

If you’re looking for a brand name of a piece of equipment, I don’t necessarily have the brand names to give you, but some test equipment can get quite expensive. I know some test equipment can be hundreds of thousands of dollars and rewuire many months lead time, six months or more lead time. Some of the test equipment is very specialized. I won’t go through the details of model numbers or specifics but, this is definitely something you need to consider when you’re getting ready for pre-commissioning. Before you arrive at site, list the test equipment that’s required, and prepare in advance for these purchases.

There can be a hesitation to purchase some of this expensive equipment, given that it’s only required for a few months of commissioning activities and may not be needed any further. And given the high price tag of some of this equipment, it can be difficult to get justification for some pieces of test equipment. One thing that I have found to be helpful, if it’s a piece of test equipment that may be required for ongoing operation and maintenance of the facilities, often the operations team or the owner will have to purchase the same equipment for operations to use regularly. If these items can be advance purchased, the commissioning team can use the same test equipment and leave it at site at the end of the project for the operating team to continue to use throughout the life of the system. I have found this is a good way to use funds efficiently and justify purchases for equipment. Talk to the groups that are involved and see if they’ve got funds allocated for some of the specialized equipment.

How do you distinguish between pre-commissioning and commissioning?

Some of the activities can blend together. There may not necessarily be a solid line between pre-commissioning and commissioning given that in the morning, you’re pre-commissioning the equipment. And by the afternoon, it’s moving into more system level testing.  Sometimes that split doesn’t necessarily exist.

But the main distinction between pre-commissioning and commissioning is that pre-commissioning is testing the piece of equipment standalone, for example just the pump or the motor tested by itself.

Commissioning is testing as a system to make sure that everything is working together, that the pump can communicate with the PLC system, and can control the valves and the chemical dosing system, and that the entire suite of a dozen instruments are working together.

To learn more about all stages of commissioning,  please read this detailed article What is Commissioning?

What do we need to inspect/check before we start energizing transformers for the first time?

There’s varying sizes of transformers. I’ve worked with small, dry type transformers and huge three phase oil filled transformers. The tests are somewhat similar, but can vary when you’ve got an oil field transformer.

Before oil is filled, an internal inspection can be done to see inside the transformer. Sometimes, you don’t necessarily want to do this, as you don’t want to be bumping or damaging any of the windings or insulation. You may choose to have a camera (GoPro on a stick) instead. We’ve done that in the past to visually verify that there was no shipping damage, or none of the supports are dislodged during shipping.

When filling the transformer with oil, you’ll take an oil sample of the new oil, and compare to a post energization sample. This confirms there is no off-gassing that contaminates the second sample due to a hotspot in the transformer. As discussed earlier, a winding resistance check can be completed, as well as a a winding ratio verification once the tap changers are set.  For large oil field transformers , there may be a control cabinet on the transformer. Several checks are verified within the control cabinet and the control systems to monitor and verify temperatures, thermal properties, and communication of the control cabinet back to PLCs and control room to verify health of the transformer.

How much earth ground should be in a transformer? 

That will depend on the design of your system. I’ll give an example because this is an interesting situation that we encountered on our last project. On an HVDC line where there are multiple operating modes, the system can operate as either bipolar or monopolar with a ground grid at either end of the line. When we were using the ground grid and injecting current into the large ground connection, the resistance of each transformer neutral in the area needs to be considered.  As current is injected into the ground grid, increased resistance in each transformer neutral causes a rise in voltage of each transformer ground connection.  This can cause power quality issues to end customers.

What is the difference between a cold loop check and hot loop check?

The difference is whether the system is energized or not. Cold loop checks are basically point-to-point checks without power applied in the loop. No communication checks can be done since it’s an un-energized cable. This confirms that the conductor is wired from the correct terminal block at one end to the correct terminal block at the other end.

Once the system is energized, you can perform the hot loop check to confirm that the PLC can communicate with the end device. If verifying MODBUS or PROFIBUS or any other protocol, this is confirmed during hot loop checks to confirm that the devices communicate with the PLC.

Once local readings on the remote device are confirmed, you can then confirm readings on the HMI. Comparing these results, you can see that the device has been calibrated and that the proper settings and ranges are applied on the HMI screen.

Open loop checks and closed loop checks can be performed. An open loop check is one-way communication to control the remote IO device from the HMI. A closed loop check confirms the return communication, verifying the status signal from the pump and that it is in fact on, looking for that closed loop feedback to see that the pump status is returned and the pump is in fact on, that would be the closed loop.

In reference to LOTO procedures, where are the NFPA Standards recommended for electrical safety?

Lock out tag out would typically be developed using industry best practices related to how the operations team operates the equipment. In a brownfield situation, the operating team may already be in place and have a lot of LOTO procedures already established. If that’s not the case, if it’s a Greenfield site, LOTO may be new to the owner, and these processes don’t exist.

In the case of a brownfield site, you must adapt to what the operations team already has in place with regards to LOTO, request for clearances, and permit to work process.  If not, then LOTO processes need to be put in place before the commissioning team mobilizeds to site. Even during the construction phase, there are lots of aspects of lock out tag out that need to take place, and that would have to be in place so that all systems can be safely  isolated for construction to take place and further commissioning to take place.

I haven’t seen that the NFPA standards come into play with regards to lock out tag out.

For EHV cable and hi-pot tests conducted, what is the criteria or standard checklist?

This will depend on your local codes and standards. Typically for a hi-pot test, double the rated voltage plus 1000 volts for one minute is applied. Applying that level of voltage for one minute and measuring, the current that’s dissipated through the dielectrics would confirm that it can meet IEEE standards. This may be different elsewhere in the world, please confirm with your technical specification.

Join our next webinar. We’re happy to share ideas and information on different topics about commissioning and startup. Your questions will be answered, and we will try our best to give you the best answers.  You can join our next live discussion at this link.

For a replay of this live webinar on electrical pre-commissioning, please watch the video below.