Switchgear & Rectifier ppt
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Switchgear and rectifiers are used to control, protect, and isolate electrical equipment. Switchgear includes disconnect switches, fuses, and circuit breakers, and is used to de-energize equipment for work and clear faults. Rectifiers convert alternating current to direct current through processes like half-wave and full-wave rectification. Common types of switchgear and rectifiers include low voltage switchgear, air circuit breakers, single-phase and three-phase rectifiers, which provide functions like electrical protection, isolation from live parts, and switching. Proper maintenance through inspection, testing, and cleaning helps ensure safe and reliable operation.
Switchgear & Rectifier ppt
- 1. SWITCHGEAR & RECTIFIER Vikas kumar 0133ec131184
- 2. SWITCHGEAR switchgear is the combination of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream.
- 3. Switchgear
- 4. Types: LV Switchgear MV Switchgear Generally electrical switchgear rated upto 1 KV is termed as low voltage switchgear The most common use of LV switchgear is in LV distribution board.
- 7. THE ROLE OF SWITCHGEAR IS : ELECTRICAL PROTECTION SAFE ISOLATION FROM LIVE PARTS LOCAL OR REMOTE SWITCHING The basic functions of Switchgear
- 8. Periodic Maintenance Preventive Maintenance a) 2 yearly Maintenance b) 4 yearly Maintenance Importance Of PM Through such PM, troubles can be detected in the Early stages and corrective actions can be taken before extensive damage occurs.
- 9. The most common use of LV switchgear is in LV distribution board. This system has the following parts Incomer The incomer feeds incoming electrical power to the incomer bus. The switchgear used in the incomer should have a main switching device. The switchgear devices attached with incomer should be capable of withstanding abnormal current for a short specific duration in order to allow downstream devices to operate. Generally Air Circuit Breakers are preferably used as interrupting device. Sub – Incomer These sub – incomers draw power from main incomer bus and feed this power to feeder bus Feeders Different feeders are connected to the feeder bus to feeds different loads like, motor loads, lighting loads, industrial machinery loads, air conditioner loads, transformer cooling system loads etc.
- 11. Busbar Busbar is a strip or bar of copper, brass or aluminium that conducts electricity within a switchboard, distribution board, substation, The cross-sectional size of the busbar determines the maximum amount of current Used to interconnect the loads and sources of electrical power.
- 12. Busbar Specification Manufacturer: Nova Magrini Gallilio Type of Busbar : Copper ( Insulated with Silver coated joints) Busbar Rating : 1500 Amp Method Of Cleaning : Clean with Lint Free Cloth Busbar Dimensions : 2*100*8 mm Busbar Maintenance Full Bus Bar Inspection check for overheating signs, visual inspection of Cu plate and nut bolts. cleaning of incoming/outgoing spouts. Remove dust with vacuum cleaner. Cleaning and lubricating mechanical links with contact grease. Check operating mechanism of shutter. Contact Resistance of Electrical joints. Check IR to earth and between phases on busbar and outgoing circuits @ 2500V
- 13. Air Circuit Breaker (ACB) A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow
- 14. Air Circuit Breakers : Charging method Circuit breaker closing springs may be compressed manually or by means of a small electric motor. The closing coil is charged by manual charging handle. For closing, first charge the spring by using the charging handle
- 15. Maintenance of Air Circuit Breaker LV Circuit Breakers operating at 600 volt and below, should be inspected Maintained every 1 to 4 years depending on their services and operating Conditions. Conditions that make frequency maintenance and inspection are necessary: High humidity and High temp Dusty or Dirty Atmosphere Corrosive Atmosphere
- 16. Inspection & Cleaning Insulating parts including bushing should be cleaned of dust Clean & inspect Arc Chutes for Cracks, Broken Parts . Replace Damage Parts Inspect Breaker Operating Mechanism for loose hardware & missing or broken etc Examine for wears Check Rack in/ out mechanism for normel operation Lubricate if necessary Check tightness of all terminations Contacts maintenance Arcing contacts to be verified for burn off To be adjusted or exchanged that arc contacts simultaneoslu when closing Permissible tolerance 1mm Adjust lead of arcing contacts from main contacts such that when arc contacts Meet then distance between
- 17. Insulation Resistance Test (Megger) Load and line conductors should disconnected from the breaker to make Test. IR between phases and phases w.r.t ground with breaker closed. the result is compared against manufacturer/ pervious data For breaker being tested. Cycling the breaker On & Off the breaker several times to check the correct operation Of breaker. Verify For Loop Check Insert circuit breaker at test position and on & off the breaker from remote location
- 18. Current Transformer A current transformer (CT) is used for measurement of alternating electric currents
- 19. Relay Relays is automatic device which senses an abnormal condition of electrical circuit and closes its contacts. these contacts in turns close and complete the circuit breaker trip coil circuit hence make the circuit breaker tripped
- 20. General Precautions to be taken Check the Electrical Isolation First During maintenance Earth MUST be connected Before maintenance of breaker spring must be discharge. Don’t use compressed air on breaker Don’t use file or emery paper for contacts cleaning Inspection Inside Switchgear Room Switchgear environment (switch room access and surrounds, including fence and external walls if outdoors. Signs of water Signs of unauthorized access Condition of firefighting equipment and warning notices General Housekeeping
- 22. INTRODUCTION • Rectifiers take a number of forms, including vacuum tube diodes, mercury-arc valves, copper and selenium oxide rectifiers, semiconductor diodes, silicon- controlled rectifiers and other silicon-based semiconductor switches • is an electrical device that converts alternating current (AC) to direct current (DC). • The process is called rectification
- 23. RECTIFIER CIRCUITS • Single-phase rectifiers –Half-wave rectification –Full-wave rectification • Three-phase rectifiers –Three-phase, half-wave circuit –Three-phase, full-wave circuit
- 24. Single-phase rectifiers: HALF-WAVE RECTIFICATION • only one half of the input waveform reaches the output which means voltage is lower • the harmonic content of the rectifier's output waveform is very large and consequently difficult to filter.
- 25. Single-phase rectifiers: HALF-WAVE RECTIFICATION • Single diode rectifier is connected across an alternating voltage source vS ▪ Since the diode only conducts when the anode is positive with respect to the cathode, current will flow only during the positive half cycle of the input voltage.
- 26. Single-phase rectifiers: HALF-WAVE RECTIFICATION The waveforms for source voltage vS and output voltage vo • The output voltage varies between the peak voltage vm and zero in each cycle. This variation is called “ripple”, and the corresponding voltage is called the peak-to-peak ripple voltage, vp-p.
- 27. Single-phase rectifiers: HALF-WAVE RECTIFICATION • If a DC voltmeter is connected to measure the output voltage of the half-wave rectifier (i.e., across the load resistance), the reading obtained would be the average load voltage Vave, also called the DC output voltage. • The meter averages out the pulses and displays this average. Output voltage and average voltage for half-wave rectifier
- 28. Single-phase rectifiers: FULL-WAVE RECTIFICATION • Full-wave rectification converts both polarities of the input waveform to pulsating DC (direct current), and yields a higher average output voltage.
- 29. Single-phase rectifiers: FULL-WAVE RECTIFICATION • Full-wave center-tap rectifier: Top half of secondary winding conducts during positive half-cycle of input, delivering positive half- cycle to load.
- 30. Single-phase rectifiers: FULL-WAVE RECTIFICATION • Full-wave center-tap rectifier: During negative input half-cycle, bottom half of secondary winding conducts, delivering a positive half- cycle to the load.
- 31. Single-phase rectifiers: FULL-WAVE RECTIFICATION • The full wave rectifier produces twice as many output pulses as the half wave rectifier. • average load voltage (i.e. DC output voltage) is found as Average DC Voltage for a Full Wave Rectifier
- 32. Multi-phase rectification • The higher the number of pulses: – the better the utilization of the rectifier – the lesser the ripple amplitude – the higher the ripple frequency — this implies that filtering the ripple is easier. • Systems with a number of pulses higher than 12 (normally obtained by combining two three- phase bridges) are not often used since their advantages are compensated by their growing complexity.
- 33. Multi-phase rectifiers: Three phase Half Wave Rectifier • consists of a three phase transformer • a star connected secondary three phase transformer with three diodes connected to the three phases • the neutral point ‘NTRL’ of the secondary is considered as the earth for the circuit and is given as the negative terminal for the load
- 34. • For each one-third of the cycle, each diode conducts. • At the instant when one diode out of three is conducting, the other two are left inactive, at that instant their cathodes becomes positive with respect to the anodes. • Then the process repeats for each of the three diodes. Multi-phase rectifiers: Three phase Half Wave Rectifier
- 35. Multi-phase rectifiers: Three phase Full Wave Rectifier • also called as a six wave half wave rectifier • in the figure below the diodes D1 to D6 will conduct only for ⅙ th of the period, with a period of
- 36. Multi-phase rectifiers: Three phase Full Wave Rectifier • the fluctuation of dc voltage is less in a three phase circuit • the variation lies between the maximum alternation voltage and 86.6% of this,
Editor's Notes
- #23: rectifiers take a number of forms, including vacuum tube diodes, mercury-arc valves, copper and selenium oxide rectifiers, semiconductor diodes, silicon-controlled rectifiers and other silicon-based semiconductor switches The most common is the semiconductor diodes used in rectifiers for power supplies. Rectifiers are mainly used in power supplies where an AC signal is to be converted to DC. The DC voltage is obtained by passing the rectifier’s output through a filter to remove the ripple (AC components). The semiconductor diode only allows one-way flow of electrons.
- #24: single-phase rectifiers are in use both as low-power stand-alone converters (up to some kilowatts) and as output stage in Switched Mode Power Supplies (SMPS). For domestic equipments. Multi-phase rectifiers- three phase rectifiers supplies the direct current at very low ripple and at a very very stable to the load (e.g., magnet or klystron) for most industrial and high-power applications, three-phase rectifier circuits are the norm. As with single-phase rectifiers, three-phase rectifiers can take the form of a half-wave circuit, a full-wave circuit using a center-tapped transformer, or a full-wave bridge circuit.
- #25: In half wave rectification of a single-phase supply, the AC power source only supplies power to the load one half every full cycle, while the other half is blocked. Because only one half of the input waveform reaches the output, mean voltage is lower. half-wave rectification is, however, a very simple way to reduce power to a resistive load. Half-wave rectifiers produce far more ripple than full-wave rectifiers, and much more filtering is needed to eliminate harmonics of the AC frequency from the output.
- #26: During the positive half cycle of the source, the ideal diode is forward biased and operates as a closed switch. The source voltage is directly connected across the load. During the negative half cycle, the diode is reverse biased and acts as an open switch. The source voltage is disconnected from the load. As no current flows through the load, the load voltage vo is zero. Both the load voltage and current are of one polarity and hence said to be rectified.
- #29: if we need to rectify AC power to obtain the full use of both half-cycles of the sine wave, a different rectifier circuit configuration must be used. Such a circuit is called a full-wave rectifier. One kind of full-wave rectifier, called the center-tap design, uses a transformer with a center-tapped secondary winding and two diodes, as in Figure above. This circuit's operation is easily understood one half-cycle at a time.
- #30: Understanding the circuit's operation one half-cycle at a time. Consider the first half-cycle, when the source voltage polarity is positive (+) on top and negative (-) on bottom. At this time, only the top diode is conducting; the bottom diode is blocking current, and the load “sees” the first half of the sine wave, positive on top and negative on bottom. Only the top half of the transformer's secondary winding carries current during this half-cycle as in Figure
- #31: During the next half-cycle, the AC polarity reverses. Now, the other diode and the other half of the transformer's secondary winding carry current while the portions of the circuit formerly carrying current during the last half-cycle sit idle. The load still “sees” half of a sine wave, of the same polarity as before: positive on top and negative on bottom. (Figure
- #32: This is the same as saying that the full wave rectifier has twice the output frequency of a half wave rectifier. For this reason, the average load voltage (i.e. DC output voltage) is found as
- #34: A three phase half wave rectifier, as the name implies , consists of a three phase transformer. Given below is a star connected secondary three phase transformer with three diodes connected to the three phases.As shown in the figure, the neutral point ‘NTRL’ of the secondary is considered as the earth for the circuit and is given as the negative terminal for the load.
- #35: The input and the output wave forms for the circuit above is shown below. For each one-third of the cycle, each diode conducts. At the instant when one diode out of three is conducting, the other two are left inactive, at that instant their cathodes becomes positive with respect to the anodes. This process repeats for each of the three diodes. The voltage between the cathode and ‘NTRL’ (dc voltage Vdc) will have a value between the peak value of alternating voltages per phase Vsm and half this value ½ Vsm.
- #36: Six diodes are used for the making of this full wave rectifier. As so, it may pose some problems and may also be advantageous in some cases. If we need a smoother output, the use of six diodes may be seen as an advantage.But the use of six diodes complicates the circuit and each diode operates for a shorter cycle.Also, since no more than six are used, the circuit is cost effective, as long as it is compared with the comparative increase in the output of the rectifier.
- #37: As shown in the output wave form, the fluctuation of dc voltage is less in a three phase circuit.The variation lies between the maximum alternation voltage and 86.6% of this, with the average value being 0.955 times the maximum value.