What is the difference between cold and hot commissioning?
Recently we got a question in our chat group about cold commissioning. That inspired us to write this short post on the difference between cold and hot commissioning. We will focus on a commissioning of a medium voltage variable speed drive system.
What is commissioning?
Commissioning is the process to put the delivered system into a regular operation ¹.
For small general-purpose drive systems of plug-and-play type this process may be a question of couple of minutes. In case of medium voltage drive systems this process usually takes few weeks. That is because the system is of larger power, contains more system components, has larger impact on the grid and other consumers, there are stricter safety precautions, the system is tailor made, application might be more demanding etc. Complex drive systems may even require several months of commissioning. In such case there is usually a site manager involved to coordinate all activities.
¹The German language uses terms Inbetriebnahme or Inbetriebsetzung (IBS) which literally means ‘take into operation’ or ‘put into operation’.
Commissioning stages
The commissioning process can be split into several phases or stages. A rough division can be into a cold commissioning and hot commissioning. In the next lines we want to explain the difference. Please note that the exact division depends on the manufacturer or supplier of the system, respectively. The companies have their internal rules and guidelines with this respect. We provide here some general characteristics that may apply for the majority of cases.
1. Cold commissioning
Cold commissioning starts when the major system components (transformer, VFD, motor, cooling system, power and control cables, filters etc) are installed. This is the first stage when putting the system into operation. This stage usually involves activities that happen before the system is connected to a medium voltage supply and energized.
This phase includes general checking of the installation, controlling the wiring and outline drawings to correspond as-built documentation, performing basic tests (e.g. insulation resistance measurement), controlling the cabling and piping or checking the individual components. Further steps may involve checking of system earthing, proving the setting of protection elements, verifying correct firmware version etc.
Significant portion of cold commissioning is to prepare the auxiliary systems (e.g. main cooling, pre-charging or pre-magnetization, oil lubrication, control supply incl. possible switch-over etc). Visual inspection is another essential part of cold commissioning. It is typically performed several times during cold commissioning stage. Any abnormality shall be investigated and rectified before moving to the next step.
Safety critical parts of the system, such as the main circuit breaker, are checked to fulfil the requirements.
Remark:
(Part of) the cold commissioning may also be called pre-commissioning in some countries or regions. Many thanks to Mr. Abdullah Qadous, Field Service Manager, for his remark.
2. Hot commissioning
The hot commissioning phase usually starts when the system is energized with medium voltage. The drive is charged, connected to the main power supply, fault free and ready to run the motor. First part of hot commissioning is normally done with uncoupled motor, i.e. sort of no-load operation. A basic VFD parameterization is done in this step. Afterwards the motor is coupled to the driven load. The system can be loaded to a certain degree (depending on the process) and fine tuning of some parameters is performed. Specific criteria are checked (e.g. switching frequency within target range, speed controller optimally tuned, motor current distortion within expected range etc). Specific commissioning tools are typically used to set the parameters, record and evaluate signals, analyse trends etc.
Customer may have specific acceptance criteria ². They are verified after the hot commissioning is finished as part of site acceptance tests.
² Performance criteria
Field service personnel
The commissioning is mostly done by field service engineers. Depending on the installation size, system complexity etc one or more engineers may work in parallel. In general, the cold commissioning part can be performed by other person than the hot commissioning. In case of long duration of commissioning, the staff on site may rotate several times. The personnel shall be well trained, certified for this type of job and supported by service specialists available remotely (typically in the service hub).
Important
Always follow national and local law valid in the installation country/region, safety guidelines of your company and the customer and installation and commissioning manuals of the equipment manufacturers. Place safety as the highest priority.
Summary
Cold and hot commissioning are two consecutive phases when putting a drive system into operation. Cold commissioning involve all kind of activities (checks, preparation work) before the system is connected to the medium voltage and energized for the first time. Hot commissioning logically follows after the cold commissioning phase. At this stage the system is already connected and supplied from the main power supply.
Cold commissioning
- Checking of installation (visual inspection, measurements, tests)
- Checking protection elements and proving the settings
- Commissioning of auxiliary systems (cooling, control, lubrication etc)
- Absence of medium voltage
Hot commissioning
- Energizing the system, connection to main power supply
- Running the motor uncoupled and coupled to the driven load
- Tuning of control parameters
- Checking the performance (criteria)
References
[1] VFD testing: Introduction, MB Drive Services, October 2020, available online, https://mb-drive-services.com/vfd_testing/
