Introduction
One automotive related factory has repeatedly complained about the tripping of overvoltage protection and power outages in some production halls. In order to find the cause and locate the fault, power quality measurements were carried out on production machines on the low voltage side. For measurements and analysis was used a three-phase network power quality analyzer Mavowatt 270.
Firstly were carried out measurements on the main electrical distribution cabinet in the plant and there were registered frequent complaints about power outages. After that, in a duration of seven days was conducted the measurement of power quality.
Analysis of measurement data
Measurements on the electrical cabinet show that voltage values oscillate at the limit (Un + 10%). At one point, there is a sudden voltage increase, then a short-term voltage interruption and again a voltage increase which lasts for more than an hour.
A detailed analysis of the diagram shows that at 05:59 a.m. there is a voltage increase from the value (Un + 9%) to the value (Un + 30.4%), which is reached at 06:04:52,25 a.m. Then occurs voltage interruption. The transient process is shown in Figure 4.
Figure 3 shows the event of exceeding the upper voltage limit value. Trends and numerical values were registered.
At 06:08:27,20 a.m. the voltage is reestablished (Un + 31.7%), as shown in Figure 2. Such a high voltage value lasts unacceptably long. Mavowatt registered these high values by 7:41 a.m.
Maintenance electricians also registered excessive voltage values. The transformers began to shake and make strange noises. During this event, there was visible damage to working machines in production plants and electrical equipment. Power supplies were damaged on CNC machines, compressors, capacitor batteries on compensating devices, etc.
After the voltage reestablishment, individual lines in the plants were successively connected to the power supply, where possible. On some lines, it was not possible to restore power supply, because the protective devices were damaged.
After such an event, it was decided to install a second network power quality analyzer for monitoring the state of voltage in the 10 kV switchyard in order to register possible adverse events in the coming hours/days and facilitate the identification of the cause of the event.
Two simultaneous measurements were initiated, on the low voltage side – machines power supply and on the high voltage side – at the 10 kV switchyard.
Measurements on the low voltage side
Figures 5, 6, and 7 show the average, maximum, and minimum voltage values after this event. All registered values are within the value range (Un ± 10%). Therefore, no voltage dips or overvoltages were registered during this measurement period.
Measurements on the 10 kV side
Figure 8 shows the average 10kV voltage values. All values are within the range (Un ± 10%). Also, the minimum and maximum voltage values remained within the same limits. No voltage dips or overvoltages were registered at the 10 kV switchyard.
CONCLUSION
This analysis includes three power quality measurements :
- Measurements on the electrical cabinet before and during the event of network overvoltage,
- Measurements on the electrical cabinet after the event of network overvoltage,
- Measurements at 10 kV switchyard after the event of network overvoltage.
o During these measurements, there was an adverse event – an increase of the network voltage to the value (Un + 31.7%) whose duration was registered in a period longerthan two hours. During this event, there were registered damages and/or failures of production machines and electrical equipment.
Overloading leads to shortened service life of the system
Considering that the overvoltage lasted longer than 2 hours, it is reasonable to suspect that some parts of electrical plants, especially power transformers, were exposed to long-lasting overvoltage. This can ultimately lead to a shortened service life of these plant components.
To factory managers is recommended to inform the supplier and distributor of electricity as soon as possible about the occurrence of the adverse event and to identify the cause of the event as well as the responsibility for the same.
Assessment of the incurred damage and possible preparation of a claim against the distributor and supplier of electricity are not the subject of this analysis.
It is recommended to purchase and install an instrument for continuous monitoring of power quality. During the monitoring of the PQ, a complete insight into all events in the network can be achieved. This makes it much easier to identify and remedy the causes of similar and other undesirable events.
