29-11-2012, 02:37 PM
THREE PHASE APPLIANCE PROTECTOR
Three Phase Appliance Protector.docx (Size: 940.47 KB / Downloads: 38)
INTRODUCTION
Many of our costly appliances require three-phase AC supply for operation. Failure of any of the phases makes the appliance prone to erratic functioning and may even lead to failure. Hence it is of paramount importance to monitor the availability of the three-phase supply and switch off the appliance in the event of failure of one or two phases. The power to the appliance should resume with the availability of all phases of the supply with certain time delay in order to avoid surges and momentary fluctuations. The complete description of a three phase appliance protector is described here. User lines connected to power supply lines can be disconnected there from by a connect/disconnect switch. An isolation rectifier circuit connected across the each phase wit operational relays. Output of the rectifier circuit controlled by a timer and through that timer operates the switch. The timer restores the connection in failure of any one or two phases.
A protection device for an electrical machine appliance or installation, comprising:
Contactor switch connected between a plurality of supply lines and respective user lines to be protected and connectable to a load. An each isolating rectifier circuit element having an input side connected across each phase side point and a neutral point which can be at a ground potential, and an output side electrically isolated from coil side of operational relay along with led and free wheeling diode. A timer connected to an coil said operational relay and connected with contactor switch for automatically disconnecting said user lines from said supply lines upon the failure of any one phase or two phases, and for automatically reconnecting said user lines with said supply lines upon presents of all the three phases with certain time delay. An each isolating rectifier circuit is connected from secondary side of each step-down transformer. And a primary side of each step-down transformer is connected from each phase to neutral.
A protection device for an electrical machine appliance or installation, comprising:
A contactor switch connected between a plurality of supply lines and respective user lines to be protected and connectable to a load. An isolating rectifier circuit element having an input side connected across secondary side of step-down transformer, and an output side electrically isolated from coil said of operational relay.
CIRCUIT ELEMENTS
RELAY:-
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism, but other operating principles are also used. Relays find applications where it is necessary to control a circuit by a low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays found extensive use in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly drive an electric motor is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protection relays".
Basic design and operation:
A simple electromagnetic relay consists of a coil of wire surrounding a soft iron core, an iron yoke, which provides a low reluctance path for magnetic flux, a movable iron armature, and a set, or sets, of contacts; two in the relay pictured. The armature is hinged to the yoke and mechanically linked to a moving contact or contacts. It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open.
Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB.
Protection diodes for relays:
Transistors and ICs must be protected from the brief high voltage produced when a relay coil is switched off. The diagram shows how a signal diode (eg 1N4148) is connected 'backwards' across the relay coil to provide this protection.
Current flowing through a relay coil creates a magnetic field which collapses suddenly when the current is switched off. The sudden collapse of the magnetic field induces a brief high voltage across the relay coil which is very likely to damage transistors and ICs. The protection diode allows the induced voltage to drive a brief current through the coil (and diode) so the magnetic field dies away quickly rather than instantly. This prevents the induced voltage becoming high enough to cause damage to transistors and ICs.
Applications:
Relays are used to and for: Control a high-voltage circuit with a low-voltage signal, as in some types of modems or audio amplifiers, Control a high-current circuit with a low-current signal, as in the starter solenoid of an automobile, Detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers (protection relays),
4-POLES CONTACTOR:
A contactor is an electrically controlled switch used for switching a power circuit, similar to relay except with higher amperage ratings. A contactor is controlled by a circuit which has a much lower power level than the switched circuit. Contactors come in many forms with varying capacities and features. Unlike a circuit breaker, a contactor is not intended to interrupt a short circuit current. Contactors range from those having a breaking current of several amps and 24 V DC to thousands of amps and many kilovolts. The physical size of contactors ranges from a device small enough to pick up with one hand, to large devices approximately a meter (yard) on a side. Contactors are used to control electric motors, lighting, heating, capacitor banks, and other electrical loads.
Operating Principle:
Unlike general-purpose relays, contactors are designed to be directly connected to high-current load devices. Relays tend to be of lower capacity and are usually designed for both normally closed and normally open applications. Devices switching more than 15 amperes or in circuits rated more than a few kilowatts are usually called contactors. Apart from optional auxiliary low current contacts, contactors are almost exclusively fitted with normally open contacts. Unlike relays, contactors are designed with features to control and suppress the arc produced when interrupting heavy motor currents. When current passes through the electromagnet, a magnetic field is produced, which attracts the moving core of the contactor. The electromagnet coil draws more current initially, until its inductance increases when the metal core enters the coil.
The moving contact is propelled by the moving core; the force developed by the electromagnet holds the moving and fixed contacts together. When the contactor coil is de-energized, gravity or a spring returns the electromagnet core to its initial position and opens the contacts. For contactors energized with alternating current, a small part of the core is surrounded with a shading coil, which slightly delays the magnetic flux in the core. The effect is to average out the alternating pull of the magnetic field and so prevent the core from buzzing at twice line frequency.
Most motor control contactors at low voltages (600 volts and less) are air break contactors; i.e., ordinary air surrounds the contacts and extinguishes the arc when interrupting the circuit. Modern medium-voltage motor controllers use vacuum contactors.
Motor controls contactors can be fitted with short-circuit protection (fuses or circuit breakers), disconnecting means, overload relays and an enclosure to make a combination starter.
Three Phase Appliance Protector.docx (Size: 940.47 KB / Downloads: 38)
INTRODUCTION
Many of our costly appliances require three-phase AC supply for operation. Failure of any of the phases makes the appliance prone to erratic functioning and may even lead to failure. Hence it is of paramount importance to monitor the availability of the three-phase supply and switch off the appliance in the event of failure of one or two phases. The power to the appliance should resume with the availability of all phases of the supply with certain time delay in order to avoid surges and momentary fluctuations. The complete description of a three phase appliance protector is described here. User lines connected to power supply lines can be disconnected there from by a connect/disconnect switch. An isolation rectifier circuit connected across the each phase wit operational relays. Output of the rectifier circuit controlled by a timer and through that timer operates the switch. The timer restores the connection in failure of any one or two phases.
A protection device for an electrical machine appliance or installation, comprising:
Contactor switch connected between a plurality of supply lines and respective user lines to be protected and connectable to a load. An each isolating rectifier circuit element having an input side connected across each phase side point and a neutral point which can be at a ground potential, and an output side electrically isolated from coil side of operational relay along with led and free wheeling diode. A timer connected to an coil said operational relay and connected with contactor switch for automatically disconnecting said user lines from said supply lines upon the failure of any one phase or two phases, and for automatically reconnecting said user lines with said supply lines upon presents of all the three phases with certain time delay. An each isolating rectifier circuit is connected from secondary side of each step-down transformer. And a primary side of each step-down transformer is connected from each phase to neutral.
A protection device for an electrical machine appliance or installation, comprising:
A contactor switch connected between a plurality of supply lines and respective user lines to be protected and connectable to a load. An isolating rectifier circuit element having an input side connected across secondary side of step-down transformer, and an output side electrically isolated from coil said of operational relay.
CIRCUIT ELEMENTS
RELAY:-
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism, but other operating principles are also used. Relays find applications where it is necessary to control a circuit by a low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays found extensive use in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly drive an electric motor is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protection relays".
Basic design and operation:
A simple electromagnetic relay consists of a coil of wire surrounding a soft iron core, an iron yoke, which provides a low reluctance path for magnetic flux, a movable iron armature, and a set, or sets, of contacts; two in the relay pictured. The armature is hinged to the yoke and mechanically linked to a moving contact or contacts. It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open.
Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB.
Protection diodes for relays:
Transistors and ICs must be protected from the brief high voltage produced when a relay coil is switched off. The diagram shows how a signal diode (eg 1N4148) is connected 'backwards' across the relay coil to provide this protection.
Current flowing through a relay coil creates a magnetic field which collapses suddenly when the current is switched off. The sudden collapse of the magnetic field induces a brief high voltage across the relay coil which is very likely to damage transistors and ICs. The protection diode allows the induced voltage to drive a brief current through the coil (and diode) so the magnetic field dies away quickly rather than instantly. This prevents the induced voltage becoming high enough to cause damage to transistors and ICs.
Applications:
Relays are used to and for: Control a high-voltage circuit with a low-voltage signal, as in some types of modems or audio amplifiers, Control a high-current circuit with a low-current signal, as in the starter solenoid of an automobile, Detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers (protection relays),
4-POLES CONTACTOR:
A contactor is an electrically controlled switch used for switching a power circuit, similar to relay except with higher amperage ratings. A contactor is controlled by a circuit which has a much lower power level than the switched circuit. Contactors come in many forms with varying capacities and features. Unlike a circuit breaker, a contactor is not intended to interrupt a short circuit current. Contactors range from those having a breaking current of several amps and 24 V DC to thousands of amps and many kilovolts. The physical size of contactors ranges from a device small enough to pick up with one hand, to large devices approximately a meter (yard) on a side. Contactors are used to control electric motors, lighting, heating, capacitor banks, and other electrical loads.
Operating Principle:
Unlike general-purpose relays, contactors are designed to be directly connected to high-current load devices. Relays tend to be of lower capacity and are usually designed for both normally closed and normally open applications. Devices switching more than 15 amperes or in circuits rated more than a few kilowatts are usually called contactors. Apart from optional auxiliary low current contacts, contactors are almost exclusively fitted with normally open contacts. Unlike relays, contactors are designed with features to control and suppress the arc produced when interrupting heavy motor currents. When current passes through the electromagnet, a magnetic field is produced, which attracts the moving core of the contactor. The electromagnet coil draws more current initially, until its inductance increases when the metal core enters the coil.
The moving contact is propelled by the moving core; the force developed by the electromagnet holds the moving and fixed contacts together. When the contactor coil is de-energized, gravity or a spring returns the electromagnet core to its initial position and opens the contacts. For contactors energized with alternating current, a small part of the core is surrounded with a shading coil, which slightly delays the magnetic flux in the core. The effect is to average out the alternating pull of the magnetic field and so prevent the core from buzzing at twice line frequency.
Most motor control contactors at low voltages (600 volts and less) are air break contactors; i.e., ordinary air surrounds the contacts and extinguishes the arc when interrupting the circuit. Modern medium-voltage motor controllers use vacuum contactors.
Motor controls contactors can be fitted with short-circuit protection (fuses or circuit breakers), disconnecting means, overload relays and an enclosure to make a combination starter.