B. System operators normally require knowledge of the state of all circuit breakers under their control. Numerical relays are the latest development in this area. This calculation is repeated for all of the quantities of interest. Relay can be broadly classified on the basis of construction and application. This comparison summarize characteristics of all protection relay types described in previously published technical articles: References: – Handbook of Switchgear – Bhel – Digital/Numerical Relays – T.S.M. Note that not all functions are found in a particular relay. It is now possible to implement a substation automation scheme using numerical relays as the main hardware provided at bay level. this portal is very helpful to all the electrical engineering student as well as professor and technical engineer.It’s very nice and helpful for all in electrical engineering to get practical knowledge & idea very easily. of starts/reaccelerations, total running time, The different software versions in existence x the differences between each version. Keypad for numeric values, through computer, Circuit breaker Auxiliary switch “Normally open” (‘a’ contact), Circuit breaker Auxiliary switch “Normally closed” (‘b’ contact), Phase angle measuring or out of step relay, Automatic selective control or transfer relay, Main-I: Non switched or Numerical Distance Scheme, Main-II: Non switched or Numerical Distance Scheme, Main-I : Non switched distance scheme (Fed from Bus PTs), Main-II: Switched distance scheme (Fed from line CVTs) With a changeover facility from bus PT to line CVT and vice-versa. Working Principle of Over Current Relay. Typical functions that may be found in a numerical relay other than protection functions are described in this section. Learn about power engineering and HV/MV/LV substations. ), Auxiliary protection functions (broken conductor, negative sequence, etc. Comparison of reliability and availability between the two methods is complex as inter-dependency of elements of an application provided by separate relay elements needs to be taken into account. The continuing reduction in the cost and size of microprocessors, memory and I/O circuitry leads to a si… No effect of Gravity on operation of static relay. This is often done using a Discrete Fourier Transform (DFT) and the result is magnitude and phase information for the selected quantity. are required to construct this protective relay.. Numeric relays, on the other hand, are programmable relays where the characteristics and behavior can be programmed. However, this technique fails when closing onto a dead but healthy line, so a level detector is also required to distinguish between current inrush due to line charging and that due to a fault. Digital sine and cosine filters (Figure 7) extract the real and imaginary components of the signal. The distinction between digital and numerical relays is particular to Protection. Other software depends on the function of the relay, but can be generalized as follows: The relevant software algorithm is then applied. The alternative is to provide each input with a dedicated A/D converter and logic to ensure that all converters perform the measurement simultaneously. Generally, there are several different types of numerical protection relays. VT supervision is made more complicated by the different conditions under which there may be no VT signal, some of which indicate VT failure and some occur because a power system fault has occurred. Get access to premium HV/MV/LV technical articles, electrical engineering guides, research studies and much more! Numerical Relays working explained in this post with the help of a Numerical relay used in industrial applications. The protection relay no longer performs a basic protection function but is an integral and major part of a substation automation scheme. The general principle is the calculation of a level of negative sequence current that is inconsistent with the calculated value of negative sequence voltage. Historically, electromechanical and static relays have been provided with fixed plug settings applied to the relay. Study specialized technical articles and papers. I think it is multi-function type? As the power of microprocessors continues to grow and pressure on operators to reduce costs continues, this trend will continue. The cheapest method is to use a single A/D converter, preceded by a multiplexer to connect each of the input signals in turn to the converter. (many literature say both are same-Digital/Numerical Relays – T.S.M. Therefore solid state relays are also called as static relays. Brief Introduction about Relay: RELAY: A Relay is a protection device that senses the fault in the circuit and gives a trip signal to the Circuit Breaker to isolate the faulty circuit. Present generation relays. However, it is sufficiently accurate for an operator to assess system conditions and make appropriate decisions. A numerical relay has the functionality that previously required several discrete relays, therefore the relay functions such as overcurrent or earth fault are referred to as ‘relay elements’. If only one or two phases are lost, the VT failure algorithm can be accomplished. If I define a Numerical Relay, honestly speaking it will seem to be quite tough but in reality they are very user friendly and easy to … For integrated protection and monitoring systems programmable microprocessor controlled static relays are preferred. Power System Protection: Static Relays. A solid state relay is composed of both static and electromechanical units in which the response is accomplished by the static units. Additionally, the input signals must be amplitude limited to avoid them exceeding the measurement range, otherwise the waveform is clipped, introducing harmonics. [info]It then has the capability to act as a disturbance recorder for the circuit being monitored, so that by freezing the memory at the instant of fault detection or trip, a record of the disturbance is available for later download and analysis. Although they are classified under different conditions their purpose remains the same, to activate the trip system when there is a fault in the electrical network. For more information on the different types of disturbance recording, read this technical article. Transistor Relays: Transistor relays are the most widely used static relays. please explain, Its very informative artical.thank you sir. Therefore the functions previously carried out by separate devices such as bay controllers, discrete metering transducers and similar devices are now found in a protection relay. This relay consists of two rectifier bridges and a moving coil or polarized moving iron relay. 2nd generation relays. Numerical results show that different reliability measures have slightly different optimum altitudes and that decode-and-forward is better than amplify-and-forward. Modern numerical relays will have comprehensive self monitoring to alert the user to any problems. Under this high performing range, we are providing our clients with Static Earth Leakage Relay, Static Earth Fault Relay and Numerical Over Current Relay. If maintenance is not carried out within a predefined time or number of trips after maintenance is required, the CB can be arranged to trip and lockout or inhibit certain functions such as auto-reclose. Site commissioning is usually restricted to running the in-built software self-check, verifying that currents and voltages measured by the relay are correct, and exercising a subset of the protection functions. The first protection devices based on microprocessors were employed in 1985. Supply is not required and all the Numerical Relay are Multi function relays. First generation numerical relays were mainly designed to meet the static relay protection characteristic, whereas modern numeric protection devices are capable of providing complete protection with added functions like control and monitoring. By organising the I/O on a set of plug-in printed circuit boards (PCBs), additional I/O up to the limits of the hardware  / software can be easily added. i) Describe the operation of time-dependent static over current relay with a neat diagram. Ok, let’s start with introduction to numerical relays, then explaining their additional features and at the end to discuss important considerations regarding software, data management, etc.. Table 1 provides a list of typical functions available, while Table 2 summarises the advantages of a modern numerical relay over static relay equivalents. Such relays are also termed as microprocessor type protective relays. Many functions previously implemented in separate items of hardware can then be included in a single item. The distinction between digital and numerical relays is particular to Protection. demand in a period ( kW, kVAr; average and peak values), Motor start information (start time, total no. It consists of one or more digital signal processors, some memory, digital and analogue input/output (I/O), and a power supply. In this relays transistors and IC’s been used, They use microprocessor. El. ALIND -The Power Movers. 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