Col. Harbin notes that many of the improvements came from XBox Generation troops asking questions and making lists of things they wanted, but key groups within. Winter 20042005 1 The timeworn method of paralleling two electrical systems by connecting them and throwing the switch can be improved upon by. Excitation Systems DECS250E Digital Excitation Control System DECS250E components are housed in a compact enclosure which makes for a simple and costeffective. Types and Applications Of Overcurrent Relay part 1 Types and Applications Of Overcurrent Relay. Types of protection. Protection schemes can be divided into two major groupings Unit schemes. Non unit schemes. Unit Type Protection. Unit type schemes protect a specific area of the system, i. The unit protection schemes is based on Kirchhoffs Current Law the sum of the currents entering an area of the system must be zero. Any deviation from this must indicate an abnormal current path. In these schemes, the effects of any disturbance or operating condition outside the area of interest are totally ignored and the protection must be designed to be stable above the maximum possible fault current that could flow through the protected area. A special employer looking for protective relay technicians. One of the most important aspects of planning and operating an electrical power system is the design of protection systems that handle fault conditions. Go back to Index 2. Non unit type protection. The non unit schemes, while also intended to protect specific areas, have no fixed boundaries. As well as protecting their own designated areas, the protective zones can overlap into other areas. While this can be very beneficial for backup purposes, there can be a tendency for too great an area to be isolated if a fault is detected by different non unit schemes. The most simple of these schemes measures current and incorporates an inverse time characteristic into the protection operation to allow protection nearer to the fault to operate first. The non unit type protection system includes following schemes Time graded overcurrent protection. Current graded overcurrent protection. Distance or Impedance Protection. Go back to Index 2. Overcurrent protection. This is the simplest of the ways to protect a line and therefore widely used. Protective Relaying For Power Generation Systems Pdf' title='Protective Relaying For Power Generation Systems Pdf' />It owes its application from the fact that in the event of fault the current would increase to a value several times greater than maximum load current. It has a limitation that it can be applied only to simple and non costly equipments. Go back to Index 2. Earth fault protection. Powerpoint 2007 Crack Product Key more. The general practice is to employ a set of two or three overcurrent relays and a separate overcurrent relay for single line to ground fault. Separate earth fault relay provided makes earth fault protection faster and more sensitive. Earth fault current is always less than phase fault current in magnitude. Therefore, relay connected for earth fault protection is different from those for phase to phase fault protection. Power+System+Relaying+Committee.jpg' alt='Protective Relaying For Power Generation Systems Pdfescape' title='Protective Relaying For Power Generation Systems Pdfescape' />Go back to Index Various types of Line Faults. No. Type of Fault. Operation of  Relay. Phase to Ground fault Earth FaultEarth Fault Relay. Phase to Phase fault Not with Ground. Related Phase Overcurrent relays. Double phase to Ground fault. Protective Relaying For Power Generation Systems Pdf MergerProtective Relaying For Power Generation Systems Pdf To DocP Protective Relay Engineering is the company that I John utilize for performing consultant and independent contract engineering work in the design, analysis, and. Revised 01022002 1 Omaha Public Power District Distributed Generation DG Manual A Guide to the Interconnection of Distributed Generation with the OPPD System. Related Phase Overcurrent relays and Earth Fault relays. Go back to Index Overcurrent Relay Purpose and Ratings. A relay that operates or picks up when its current exceeds a predetermined value setting value is called Overcurrent Relay. Overcurrent protection protects electrical power systems against excessive currents which are caused by short circuits, ground faults, etc. Overcurrent relays can be used to protect practically any power system elements, i. For feeder protection, there would be more than one overcurrent relay to protect different sections of the feeder. These overcurrent relays need to coordinate with each other such that the relay nearest fault operates first. Use time, current and a combination of both time and current are three ways to discriminate adjacent overcurrent relays. Over. Current Relay gives protection against Overcurrent includes short circuit protection, and short circuits can be Phase faults. Earth faults. Winding faults. Short circuit currents are generally several times 5 to 2. Hence fast fault clearance is always desirable on short circuits. Go back to Index Primary requirement of Overcurrent protection. The protection should not operate for starting currents, permissible overcurrent, current surges. To achieve this, the time delay is provided in case of inverse relays. The protection should be co ordinate with neighboring overcurrent protection. Overcurrent relay is a basic element of overcurrent protection. Go back to Index Purpose of overcurrent Protection. These are the most important purposes of overcurrent relay Detect abnormal conditions. Isolate faulty part of the system. Speed Fast operation to minimize damage and danger. Discrimination Isolate only the faulty section. Dependability reliability. Security stability. Cost of protection against cost of potential hazards. Go back to Index Overcurrent Relay Ratings. In order for an overcurrent protective device to operate properly, overcurrent protective device ratings must be properly selected. These ratings include voltage, ampere and interrupting rating. If the interrupting rating is not properly selected, a serious hazard for equipment and personnel will exist. Current limiting can be considered as another overcurrent protective device rating, although not all overcurrent protective devices are required to have this characteristic. Voltage Rating The voltage rating of the overcurrent protective device must be at least equal to or greater than the circuit voltage. The overcurrent protective device rating can be higher than the system voltage but never lower. Ampere Rating The ampere rating of a overcurrent protecting device normally should not exceed the current carrying capacity of the conductors As a general rule, the ampere rating of a overcurrent protecting device is  selected at 1. Go back to Index Difference between Overcurrent and Overload protection. Overcurrent protection protects against excessive currents or currents beyond the acceptable current ratings, which are resulting from short circuits, ground faults and overload conditions. While, the overload protection protects against the situation where overload current causes overheating of the protected equipment. The overcurrent protection is a bigger concept So that the overload protection can be considered as a subset of overcurrent protection. The overcurrent relay can be used as overload thermal protection when protects the resistive loads, etc., however, for motor loads, the overcurrent relay cannot serve as overload protection Overload relays usually have a longer time setting than the overcurrent relays. Go back to Index Types of Overcurrent Relay. These are the types of overcurrent relay Instantaneous Overcurrent Define Current Relay. Define Time Overcurrent Relay. Inverse Time Overcurrent Relay IDMT RelayModerately Inverse. Very Inverse Time. Extremely Inverse. Directional overcurrent Relay. Go back to Index 1. Instantaneous Overcurrent relay Define CurrentDefinite current relay operate instantaneously when the current reaches a predetermined value. Instantaneous Overcurrent Relay Definite Current. Operates in a definite time when current exceeds its Pick up value. Its operation criterion is only current magnitude without time delay. Operating time is constant. There is no intentional time delay. Coordination of definite current relays is based on the fact that the fault current varies with the position of the fault because of the difference in the impedance between the fault and the source. The relay located furthest from the source operate for a low current value. The operating currents are progressively increased for the other relays when moving towards the source. It operates in 0. Application This type is applied to the outgoing feeders. Go back to Index 2. Definite Time Overcurrent Relays.