Overcurrent protection study for power network (solving relay setting miss-coordination)

The quality of protection

The basic function of electrical protection is to detect system faults and to clear them as soon as possible. For any one particular application, there are many ways to do this function, with varying degrees of effectiveness. The choice is influenced by the overall protection philosophy of the plant, and the importance of the equipment or portion of the network to be protected, weighing cost against performance.

The general philosophy of applying protection in a power network is to divide the network into protective zones, such that the power system can be adequately protected with the minimum part of the network being disconnected during fault conditions.

The zones can either be very clearly defined, with the protection operating exclusively for that zone only as in differential protection, illustrated in Figure 1.

The zones can be less clearly defined, with overlapping of the protection function between zones for example, overcurrent protection, as illustrated in Figure 2.

Numerical Relays

The distinction between digital and numerical relay rests on points of fine technical detail, and is rarely found in areas other than Protection. They can be viewed as natural developments of digital relays as a result of advances in technology. Typically, they use a specialized digital signal processor (DSP) as the computational hardware, together with the associated software tools.

The input analogue signals are converted into a digital representation and processed according to the appropriate mathematical algorithm. Processing is carried out using a specialized microprocessor that is optimized for signal processing applications, known as a digital signal processor or DSP for short.

By using multiple microprocessors to provide the necessary computational performance, a large number of functions previously implemented in separate items of hardware can now be included within a single item.

Case Study: Baleela Oil-Field Network

In power systems, the analysis of the network is an important step to determine the performance, both under normal operation and during faults conditions. Fault levels at different parts of the network, as well as protection coordination are some of the many important parameters that define the performance of the network.

Site Overview

A site visit was conducted to Baleela Oil-Field network in order to collect the data of the existing network, collect the uploaded settings of the protection system and investigate the defects of the existing settings.

The following data was collected:

1. Details of 33kV and 11kV substations in the network.
2. Single line diagram of the Baleela Power system network.
3. Impedances of all transmission lines and transformers.
4. Reactance and MW rating of all generators connected to the network.
5. Load details (MVAr and MW) of the existing network.
6. Length and type of transmission lines from one substation to another.

The collected data old settings is shown in appendix A and B respectivly.