Power System Protection & Relaying: Brief Notes, Lecture notes of Computer System Design and Architecture

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MP 7202: Power

System Protection &

Relaying

Brief Notes Dr. M. Edimu 2018

Detailed Course Content:

• (^) Introduction: Protection Basics, Instrument Transformers, Grounding schemes and fault detection and identification, Coordination, Symmetrical Components
• (^) Distribution Protection: Instantaneous overcurrent protection, Time overcurrent protection, Directional protection,
• (^) Bus protection: Differential Protection, Bus configurations, Common bus protection schemes, Impacts of CT saturation,
• (^) Transmission Protection: Distance Protection Basics, Distance element designs Past papers for revision
• (^) Fundamentals for software tools and labs: Introduction to Network simulation for protection systems (using DigSilent)

Course Assessment

Activity Contributio n to final mark 1 lectures week 2 tests 15% Assignments Practical work (10%), Project work (10%), Group work (5%)

Examination 60%

Power system studies

• (^) 1. Load flow: System status (VR, Power flow, pf, overload)
• (^) 2. System Stability: Energy balance
  • (^) Steady state, transient state and dynamic state analyses
• (^) 3. Short circuit analyses: Make or break fault levels. - (^) Ratings of protection equipment Type of faults and their characteristics Fault Ride through Curve

Need for Protective

Apparatus

• (^) A power system(PS) must
  • (^) (a) meet present load and
  • (^) (b) be capable to meet future demands.
• (^) Hence PS generation system is designed for (a) and (b).
• (^) The transmission and distribution systems of the PS must be able to deliver the required power to the load under all conditions without major breakdowns.

Need for Protective

Apparatus

• (^) The first step of implementation is to ensure the system components to be robust i.e. most reliable and requiring minimum, or best still nil, maintenance.
• (^) Secondly, the design and maintenance team must analyze the possible consequences of system failure that may lead to complete shutdown, long system outage, or very slow return to normal system operation.

Need for Protective

Apparatus

• (^) Further analysis of this means power flow modification/diversion may be made to ensure that load conditions are still met
• (^) It is noted that special equipment are installed as part of the system to detect, isolate and remove faults or faulty area. They are installed in various strategic sections during the design stages or may be introduced during upgrading or system improvement. They are referred to as “protective equipment or protective relay”.

Need for Protective

Apparatus

• (^) A protective relay is the device that offers instruction/command to disconnect/isolate a faulty part of the system but also ensures that the rest of the system is protected from damage and power flow continues in the healthy part(s) of the system.

Power system

transducers

• (^) Hence as far as a power system is concerned, from energy generation to consumption, there are several power system transducers.
• (^) It is noted that their performance is to deliver reliable power from generation to consumption. The process of delivery is referred as “power system performance”
• (^) Protection system require voltage/current to operate. CTs and VTs used to transform, proportionately, voltage and current to levels required

Fundamental principles of power

system protective devices

• (^) The fundamental principles of protective devices are to: 1. Ensure detection of any abnormal behavior/fault of the system. 2. Isolate the abnormal part of the system. 3. Remove the cause of the abnormality. 4. Restore the system to pre- or post-fault normal conditions. 5. Ensure the safety (no effect) of other equipment in the vicinity. 6. Ensure safety of operators and non-operators of the power system.

Primary and Backup Protection

Systems.

• (^) It’s without any compromise that a power system MUST operate within specific limits (e.g. 50Hz ± 2%).
• (^) The demand at the load end is that power must be available UNDER ALL CIRCUMSTANCES e.g. enough power at all times and under changing/unpredicted circumstances and/or conditions.

Primary and Backup Protection

Systems.

• (^) Let’s examine
• (^) 1. The basic requirements of protection:
• (^) A protection apparatus or device must function such that it - (^) (i) safeguards the entire system to maintain supply continuity of specified quality - (^) (ii) minimizes damage and hence reduces repair costs and time - (^) (iii) ensures safety of personnel and non- personnel.

Primary and Backup Protection

Systems.

• (^) Selectivity : To detect & isolate the faulty area (items).
• (^) Stability : To leave the healthy areas (parts or circuitry) intact to ensure continued system operation and power supply.
• (^) Sensitivity : To detect even the minute fault (current or voltage abnormalities); which may result into huge damages.
• (^) Speed : To operate speedily so as to minimize damage to the rest of the system and ensure safety to personnel and non-personnel.
• (^) Dependable: To trip as and when required.
• (^) Secure: Must NOT trip falsely.

Primary and Backup Protection

Systems.

• (^) The above stringent (without exceptions) requirements means a protection scheme that is not allowed to fail.
• (^) While power systems are designed, their protection is inbuilt and intrinsic. This is the Primary Protection. However, practice has shown that, despite the satisfactory operation of the primary protection, system failures have occurred sometimes leading to disastrous consequences e.g. complete shutdown.