Static Relays contains electronic circuitry (Diodes, transistors, zener diodes, thyristors,logic gates …etc) ICs are widely being used in place of transistors as there are more reliable and compact comparator circuit compares V or I Comparator o/p applied to slave relay (Semi static) thyristor circuit (Fully static) Slave relay is EM relay which closes the contacts EM slave relay provides no. of o/p contacts at low cost Multi contact triggering arrangements are simple with EM relays
Classification of Static Relays Part of the circuitry which compares two actuating quantities is comparator Actuating Quantities – Magnitudes of V or I (or corresponding derived quantities) – Phase angle between V and I (or corresponding derived quantities) Amplitude Comparator compares the amplitude irrespective of angle between quantities Relay sends trip signal when operating quantity exceeds restraining quantity Phase comparator compares the phase angle irrespective of the magnitudes Relay sends trip signal when the phase angle between them < 90 0
Amplitude Comparators
Phase Comparators
Duality between comparators
Amplitude comparator used for phase comparison
Duality between comparators
Phase comparator used for amplitude comparison
Merits & Demerits of Static relays
Types of Amplitude & Phase Comparator Amplitude Comparators 1.Circulating Current type rectifier bridge comparators 2.Phase splitting type comparators 3.Sampling comparators Phase Comparators 1.Vector product phase comparator 2.Coincidence type phase comparators 1.Phase Splitting Type 2.Integrating Type 3.Rectifier bridge type 4.Time-bias type
Rectifier Bridge Type Amplitude Comparator
Phase Splitting Type Amplitude Comparator
Phase Splitting Type Phase Comparator
Integrating Type Phase Comparator
Rectifier Bridge Type Phase Comparator
Time bias type phase comparator
Static instantaneous over current relays
Static Definite time over current relay
Static Inverse time over current relay
Static Directional Over current relay
Why Numerical Relaying? To improve dependability as well as security Self checking facility Immune to variation in parameters of individual components Very low burden More flexibility because of programmable capability
Why Numerical Relaying? Contd.... Fibre optical communication with substation LAN Adaptive relaying schemes Permit Historical data storage Allow GPS (Geographical Positioning System) Time stamping
Why Numerical Relaying? Contd.... Numerical relays simplify interfacing with CTs and VTs Separate connection is not required, zero sequence voltages and currents can be derived inside the processor
Why Numerical Relaying? Contd.... Finally, Numerical relays represent best compromise between: economy and performance dependability and security complexity and simplicity speed and accuracy credible and conceivable
Analog Input Subsystem Simultaneous Sampling Scheme
Sample and Hold Circuit A S & H circuit which conceptually is a shunt capacitor with a switch holds the information (in terms of voltage)
Simultaneous Sampling Scheme: MUX Multiplexer is a collection of analog switches, which can be selected by supplying binary code Typically, power system applications involve more than one analog input To reduce the cost of the hardware, multiple channels are multiplexed through analog multiplexer to a single ADC Accuracy of the analog multiplexer depends on load impedance at the output terminal As S & H circuit has impedance in the range 10^8 to 10^12, no problem is encountered
Simultaneous Sampling Scheme All S & H amplifiers are set to hold state simultaneously This preserves the relative phase information between multiple analog signals Successive ADC which have a conversion time of μ-sec An Anti-Aliasing filter is a low pass filter (LPF) used to cut-off the high frequency content in the input signal, connected after signal conditioning hardware
Schematic diagram of Typical Numerical Relay
Comparision between Electromechanical and Numerical Relays
Static Impedance Relay using Amplitude comparator
Static Reactance Relay
Static Mho Relay