Читать книгу Practical Power Plant Engineering - Zark Bedalov - Страница 29

RR is also shown in Figure 1.6. This is a big commissioning event as the unit enters the operation and starts producing electricity. Typically, RR is applied to power plants but not to the industrial plants. RR lasts anywhere from 7 to 30 days. A period of 30 days is the most common RR period. For the plant to enter an RR, it means it has been fully commissioned and proven to be operational, with some minor listed deficiencies that do not affect the production. These can be fixed during the RR or later. Successful RR leads to ownership transfer and a start of a one to two years warranty period.

During an RR, the owner's operators take over the plant operation in the presence of the suppliers in supervisory role. This is also a phase of practical training for the operators. The operators follow the directives of the dispatch center and load the machines accordingly in terms of MW and MVARs. The intent is to operate and expose the plant to all the operating modes and transitions without restrictions and as often as possible. As more and more automation and supervision is added to the plants the commissioning and RR tests get more and more involved.

Each plant owner may dictate different constraints for RR. The rules may also depend on the unit performance during the commissioning. If the plant has been failing often, owners may impose more stringent conditions. In general, the unit must operate 30 days, 24 hours a day without a major failure that would cause the unit to reduce its capability to carry load. If that happens, the RR is restarted from the beginning. For instance, a failure of a pump with a successful automatic transition to the healthy pump will not be a cause to stop the RR, but considered a successful operating action.

It is much easier to commission a plant if you had followed it through the design and construction into commissioning. Sometimes a commissioning engineer may be invited to do a commissioning on a plant that he/she may not be familiar with. There were a number of cases like this. One of difficult ones was in Lahore, Pakistan, where we were invited to conduct a commissioning and RR test after it has failed in 12 earlier attempts over a period of two years. It was a 5 × 30 MW thermal plant.

During the RR, the plant was supposed to operate flawlessly for seven days without a single alarm while being tested under all the operating conditions. In addition, there was a specific test during the RR while all the plant units were running, called “Islanded Test.” An unexpected three‐phase fault is arranged on the HV line, connected to the plant. To pass the test, the plant had to separate itself from the grid, shutting down four units, while one unit was supposed to be left running and maintaining the plant station service load.

Well, this time, it worked well, and the plant passed the test. We knew that this time, we had to take a different approach. We modified the protective relay settings and readjusted the governor transfer functions. Every short circuit is different, and the units are required to conform accordingly. Perhaps we were just plain lucky. It is hard to tell. This time the protective relays operated selectively and the new governor settings acted correctly.