Question

Voltage sag is considered the most costly PQ event. Basically, it affects most of the process facilities in the plant. The EPD SDN BHD is a plastic plant. The plant is very diligent in monitoring the power system. They identify the fact that the voltage sag has occurred over the past 5 years. The total number of voltage sag is 14 events per year and causes damage to the facility. They also identified the fact that they loss RM 120, 000 ringgit per event due to this equipment. The plant does post-event cleaning.
a) Explain with suitable justification which equipment has been used by this plant to measure and record the occurrence of voltage sag in a year.

b) The management of the plant intends to double the size of the plant because they cannot keep up with the production. Suggest a good solution; how this plant could solve the PQ problem and minimize the loss.

c) The solution for part b) may be expensive, and they cannot effort any capital for this solution. As a technical advisor how could you convince the management of the plant such that they can listen to you?

Answer 1

a) To Record the Voltage Sag:

Uninterruptible power supplies (UPSs) are extremely popular for computers: personal computers, central servers, and process-control equipment. For the latter equipment the costs of a UPS are negligible compared to the total costs. Motor-generator sets are often depicted as noisy and as needing much maintenance. But in industrial environments noisy equipment and maintenance on rotating machines are rather normal. Large battery blocks also require maintenance, expertise on which is much less available. Voltage source converters (VSCs) generate a sinusoidal voltage with the required magnitude and phase, by switching a de voltage in a particular way over the three phases. This voltage source can be used to mitigate voltage sags and interruptions.

Use a power-quality meter to gather a full record of voltage dips, swells or transients. An exact timestamp, detailed event profile and high-resolution waveform capture provided by higher-quality meters enables correlating the event to a machine state and finding the root cause of machine problems.

b) Solving PQ problem :

•From Fault to Trip

•Reducing the number of faults

Increase the insulation level. This generally reduces the risk of short-circuit faults. Note that many short circuits are due to over-voltages or due to a deterioration of the insulation.

Increase maintenance and inspection frequencies. This again generally reduces the risk of faults. If the majority of faults are due to adverse weather, as is often the case, the effect of increased maintenance and inspection is limited.

•Reducing the fault clearing time

•Reducing the fault-clearing time does not reduce the number of events but only their severity. It does not do anything to reduce the number or duration of interruptions.

•The duration of an interruption is determined by the speed with which the supply is restored. Faster fault-clearing does also not affect the number of voltage sags but it can significantly limit the sag duration.

•The ultimate reduction in fault-clearing time is achieved by using current-limiting fuses. Current-limiting fuses are able to clear a fault within one half-cycle, so that the duration of a voltage sag will rarely exceed one cycle.

•Faster backup protection is one of the few effective means of reducing fault clearing time in transmission systems. Possible options are to use intertripping for distance protection, and breaker-failure protection.

•Improving Equipment Immunity

•The immunity of consumer electronics, computers, and control equipment (i.e., single-phase low-power equipment) can be significantly improved by connecting more capacitance to the internal dc bus. This will increase the maximum sag duration which can be tolerated.

•Single-phase low-power equipment can also be improved by using a more sophisticated dc/dc converter: one which is able to operate over a wider range of input voltages. This will reduce the minimum voltage for which the equipment is able to operate properly.

•Improving the immunity of dc adjustable-speed drives is very difficult because the armature current, and thus the torque, drops very fast. The mitigation method will be very much dependent on restrictions imposed by the application of the drive.

c) The above techniques or necessary steps need to be taken in order to run this plant efficiently. By using the above steps, the cost may be high at this point but the loss of production will not be happened for life time. If we loss our clients or customers due to lack of delivery then we cant bring them again. We should need to hold them we should also need to add few more clients or customers which makes our company in developing. It is possible only if we run the plant without any disturbance which is only possible by the above steps.