Technical guide protection criteria for medium voltage. Maximum overcurrent protection mop first, a basic calculation is made, and then a number of filters or conditions will alter the computed mop value to arrive at the final value that appears on a product nameplate. Overcurrent coordination page 3 qualtech engineers, inc. Rather, a device with an interruption rating of 10,000 amps is certified to be able to stop a.
The three major categories or types of overcurrent are overload, shortcircuit, and groundfault. In this section we will consider only the latter two aspects. Power system protection with relay coordination mehulkumar d. States that overcurrent protection shall be omitted where the opening of the control circuit would create a hazard, as for example, the control circuit of a fire pump motor and the like. Step 3 branch circuit overcurrent protection sizing 430152 select type of motor and type of over current protection device from the chart and multiply values given by the flc of the motor. Fast protection minimizes temperature rise mechanical damage from magnetic forces voltage sag transient stability issues shock and arcflash hazards. The proper application of overcurrent protection rules for airconditioning and refrigeration equipment can be made relatively easy by following a few basic steps as outlined in this article. If ambient temperature andor more than three conductors are involved, then calculate wire ampacity needed from table from the following formula. Mca and mop what are they and how are they calculated. The fla on the motor nameplate is a rating from the motor manufacturer and is of not used in this calculation. However, this isnt usually the best choice for motors. It contains a full range of selectively enabled, self contained protection and control elements as detailed in the functional block diagram and features table. The general rules for overcurrent protection of conductors and equipment are found in article 240 of the national electric code.
First, a basic calculation is made, and then a number of filters or conditions will alter the computed mop value to arrive at the final value that appears on a product nameplate. This decides the range available for setting relay pickup. Mohammed tawfeeq overcurrent protective relays overcurrent relays overcurrent relaying is the simplest and cheapest type of protection used for protection of lines, transformers, generators and motor. Thermal memory for block and trip function with the settable cooling time up to 200 minutes.
To illustrate this, lets use the same motor as in the previous example. Recommendations for overcurrent protection ul and csa north american standards, continued secondary voltage overload protection hammond transformers va rating 50 75 100 150 250 350 500 750 1500 2000 3000 5000 12 125% 5. The rej 523 is based on a microprocessor environment. Due to the long lead time for repair of and replacement of transformers, a major goal of transformer protection is limiting the damage to a faulted transformer. Modular, compact design overcurrent reduction setting for maintenance dynamic thermal modeling 4line, 80.
Methodology overcurrent protection the protection in which the relay picks up when the magnitude of current exceeds the expected pickup value. Calculate the instantaneous element setting for the relay shown. When the protection device values determined from table 430. Oct 27, 2017 get an intro to overcurrent protection and ocpds overcurrent protection devices. Equipment damage, personal injury, and even death can result from the improper application of a devices voltage rating, current rating, or. Overcurrent protection devices are meant to protect against the potentially dangerous effects of overcurrents, such as an overload current or a shortcircuit current, which creates a fault current. The basic element in overcurent protection is the overcurrent relays. The protection normally provided that coordinates with the damage curve is typically an inverse time overcurrent device such as a fuse or relay.
Five independent output relays selectable for in service. The ansi device number is 50 for an instantaneous overcurrent ioc or a definite time overcurrent dtoc and 51 for the inverse definite minimum time. This is called the branchcircuit shortcircuit and groundfault protection and is determined using table 430. Considerations in choosing directional polarizing methods for ground overcurrent elements in line protection applications technical report to the line protection subcommittee of the pes, power systems relaying committee completion date.
Overcurrent protection over current protection is the current protection device action when the current exceeds a predetermined maximum. Section 2402 indicates article 440 shall be used for protection of airconditioning and refrigerating equipment. Mohammed tawfeeq overcurrent protective relays overcurrent relays overcurrent relaying is the simplest and cheapest type of protection used for protection of. Circuit protection is required to help prevent fires from occurring due to. To avoid using over sized conductors, overcurrent devices should be selected at about 110 to 125 percent of the transformer fullload current rating. Recommendations for overcurrent protection ul and csa. In short, the basic mop is calculated by multiplying the rated current of the largest motor times. Overcurrent protection fundamentals cedengineering. Overcurrent protection fundamentals r ced engineering. The ultimate true safety factor can be calculated using the. Thanks for the detailed explanation on overcurrent setting calculations. Unit 6 conductor sizing and protection calculations. Size the overcurrent protection device in accordance with sections 240. Combined optimal distance to overcurrent relay coordination, international conference on power electronics, drives and energy systems pedes, 2012, ieee.
Overcurrent protection for airconditioning and refrigeration. Calculating overcurrent protection, transfer switches and. Personnel injury protection equipment damage protection coordination and proper discrimination of operation. Ocpd servicing and maintenance industrial control panels electrical safety fuses for hazardous locations photovoltaic systems and fuses. Maximum overcurrent protection mop is a bit more complicated. The overcurrent protection device, either a breaker or fuses, must be sized to prevent the unit from drawing more current than the mop. One should study the diagram to develop an understanding. The protection relay adjustments are first calculated to provide the shortest tripping times at maximum fault currents and then verified to understand if tripping will. To better understand the code rules, the characteristics of these types of motors must be understood. Would you please, compare and contrast these same calculation with the ones done to get the settings of an rej603 abb protection relay. How to size an overcurrent device for a transformer sciencing.
Low voltage breaker fuse coordination requires a minimum 0. How to size an overcurrent device for a transformer. Overcurrent and earthfault relay rej 515 service and. In this article, we will cover types of overcurrent, what overcurrent protection devices are, and their place in an electrical circuit. Circuit protection is required to help prevent fires from occurring due to overcurrent faults or short circuits. Get an intro to overcurrent protection and ocpds overcurrent protection devices. This module is used for the coordination of various overcurrent protection devices in a given network. Motor protection unit advanced motor protection model for larger, complex motors. The secondary winding overcurrent protection is typically set with two steps. Table 2 details the calculations associated with setting of overcurrent relays. The three primary aims of overcurrent electrical protection are.
The combined overcurrent and earthfault relay rej 515 is a secondary relay which is connected to the current transformers of the object to be protected. The table shows the maximum over current as a percentage of the transformer current. Overcurrent protection in ac power systems technical. The branchcircuit overcurrent protection device must be sized not less than 125% of 53 amperes, so, branchcircuit overcurrent protection device size 53 amperes x 125% 66 amperes. Conductor sizing and protection calculations unit 6 an overcurrent device protects the circuit by opening the device when the current reaches a value that will cause excessive or dangerous temperature rise overheating in conductors. For a polyphase motor, when using an inverse time breaker, you are permitted to use a rating 250 percent of the motor fullload current shown on the motor full. There are a variety of concepts by which this task is done. Negative sequence overcurrent relay and protection assemblies rxiik 4 and raiik 400 nite time 0100 seconds.
Phasor calculation protection methods relay logic modify if required trip order no trip. Difference between overcurrent protection and overload. Understand basic protection principles overcurrent 50, 51, 50n, 51n. Oct 11, 20 thanks for the detailed explanation on overcurrent setting calculations. The response of the overcurrent protection devices is visualized in the timecurrent characteristic tcc curve. Overcurrent protection devices will, of course, either blow or trip under such conditions, but their interruption ratings have nothing to do with the current at which they open. Directional non directional overcurrent protection. Considerations in choosing directional polarizing methods. It may be the primary the only protection used to clear the throughfault, or it may be the backup protection to another primary device or system that detects and clears the fault highspeed. With over 250 pages, this industryleading handbook has new or expanded information on the following. Overcurrent devices must have an interrupting rating sufficient for the maximum possi. Overcurrent relay protection is given at b, c, d and e, that is, at the infeed position of each part of the electrical power system. Basically, in the phph fault, relative to phground fault, note that both v quadrature and i fault have shifted by 30.
A forth earth fault threshold is used for derived current calculation when no earth ct available. Use of the relay the overcurrent relay rej 523 is intended for selective shortcircuit protection in medium voltage distribution networks but can also be used for protection of generators, motors and transformers. Threephase overcurrent protection 5051 earth fault overcurrent protection 50n51n three independent stages are available for phase and earth fault protection. Column 4 optimal branch circuit protection there are two distinct levels of protection philosophy provided in this column. Overcurrent relays is the simplest and cheaper type of protection used for lines, transformers, generators and motor. They also protect circuits downstream from the transformer. Pdf an overcurrent protection relay based on local measurements. Each relay protection device comprises a definitetime delay overcurrent protection relay in which the trip of the current sensitive element starts the time delay device. Neplan overcurrent protection selectivity analysis back to overview. Supply wiring must be rated to carry at least the amps shown as mca. Overcurrent relay setting model for effective substation. May 2015 members, working group d3 considerations in choosing directional polarizing methods for ground. Calculation of phase fault overcurrent relay settings.
Overcurrent relaying is the simplest and cheapest type of protection used for protection of lines. How we calculate mca and mop these two values are published on the nameplate to insure proper wire sizing and safe operation. Negative sequence overcurrent relay and protection. Considerations in choosing directional polarizing methods for.
If relay r2 is expected to provide backup protection for. The overcurrent unit and the earthfault unit continuously measure the phase currents and the neutral current of the object. A forth earth fault threshold is used for derived current calculation when no earth ct available the first and second stage can be independently. For an effective substation protection scheme, a time delay should be made to exist between the main and back up protection system.
Time overcurrent relays fall 2018 u i ece525 lecture 11 directional steptime overcurrent ansi 67 the directional overcurrent relay can be perceived as a type 50 instantaneous element controlled by a type 32 directional element if the type 67 relay element is to provide backup protection, they use definite time delay for downstream coordination. The best method for providing overcurrent protection for most circuits is to use a circuit breaker that combines overcurrent protection with shortcircuit and groundfault protection. Provides current and temperature protection, data logging, and metering. Based on operating time characteristics, normally defined by the time vs. Overcurrent protection worksheet basic electricity.
And when using such smaller overcurrent protection, devices should be of the timedelay type on the primary side to compensate for inrush currents which reach 8 to 10 times the fullload primary. In order for a trip to occur, the magnitude of the operate. Pdf power grid overcurrent relays are used to protect the interphase faults as well as. Overcurrent protection an overview sciencedirect topics. The protection normally provided that coordinates with the damage curve is typically an inverse timeovercurrent device such as a fuse or relay. Circuit breakers protect transformers from overcurrent situations and short circuits. Motor control circuit protection cooper industries. Calculation minimum phase voltage magnitude minimum phasetophase voltage magnitude. Overcurrent protection for electrical equipment can be accomplished by several different methods. Long time settings of overcurrent devices are above the maximum expected full load current for that device. The basic element in overcurrent protection is an overcurrent relay. Once the circuit breaker opens or trips due to a short circuit or some other overcurrent scenario, the circuit.
Overcurrent relay coordination for phase and earth faults using etap proceedings of 7 th irf international conference, 27 april2014, pune, india, isbn. Medium voltage products technical guide protection. Medium voltage products technical guide protection criteria. Most ground directional overcurrent relays can be thought of as having two components, a directional component and an overcurrent component. Overcurrent protection is protection against excessive currents or current beyond the acceptable current rating of equipment. Introduction transformers are a critical and expensive component of the power system. Overcurrent relay setting model for effective substation relay coordination international organization of scientific research 27 p a g e associated with temperature rise of the equipment whose permissible limit is based on insulation class and material problems. Overcurrent protection in ac power systems technical articles. If the calculated value does not correspond to a standard fuse or breaker size listed in 2406 then you are allowed to go up to the next higher size.
1216 1226 657 251 1368 662 1170 777 1021 300 98 1648 652 143 127 910 1472 722 1592 352 106 423 1044 883 904 237 165 1211 1289