Main Equipment of Switch Gear and Their Working

November 1, 2021 by Opal Isaac Posted in Electrician Talk

Equipment of Switch Gear

Following are the main Equipment of Switch Gear,

1) Switches

A switch is main equipment of switch gear, it is a device which is used to open or close an electrical circuit in a convenient way. It can be used under full-load or no-load conditions but it cannot interrupt the fault currents. When the contacts of a switch are opened, an arc is produced in the air between the contacts. This is particularly true for circuits of high voltage and large current capacity.
The switches may be classified into:

a) Disconnector (or isolator)

This switch is a manually-operated, lockable, two-position device (open/closed) which provides safe isolation of a circuit when locked in the open position. Its characteristics are defined in IEC 60947-3. A disconnector is not designed to make or to break current and no rated values for these functions are given in standards. It must, however, be capable of withstanding the passage of short-circuit currents and is assigned a rated short-time withstand capability, generally for 1 second, unless otherwise agreed between user and manufacturer. This capability is normally more than adequate for longer periods of (lower-valued) operational over current, such as those of motor-starting. Standardized mechanical-endurance, over voltage, and leakage-current tests, must also be satisfied.

b) Load-breaking switch

This control switch is generally operated manually (but is sometimes provided with electrical tripping for operator convenience) and is a non-automatic two-position device (open/closed). It is used to close and open loaded circuits under normal unfaulted circuit conditions. It does not consequently, provide any protection for the circuit it controls.
IEC standard 60947-3 defines:
The frequency of switch operation (600 close/open cycles per hour maximum)
Mechanical and electrical endurance (generally less than that of a contactor)
Current making and breaking ratings for normal and infrequent situations

When closing a switch to energize a circuit there is always the possibility that an unsuspected short-circuit exists on the circuit. For this reason, load-break switches are assigned a fault-current making rating, i.e. successful closure against the electrodynamic forces of short-circuit current is assured. Such switches are commonly referred to as “fault-make load-break” switches. Upstream protective devices are relied upon to clear the short-circuit fault.

c) Remote control switch

This device is extensively used in the control of lighting circuits where the depression of a pushbutton (at a remote-control position) will open an already-closed switch or close an opened switch in a bi-stable sequence.
Typical applications are:
• Two-way switching on stairways of large buildings
• Stage-lighting schemes
• Factory illumination, etc.
Auxiliary devices are available to provide:
• Remote indication of its state at any instant
• Time-delay functions
• Maintained-contact features

2) Fuses

Fuses exist with and without “fuse-blown” mechanical indicators. Fuses break a circuit by controlled melting of the fuse element when a current exceeds a given value for a corresponding period of time; the current/time relationship being presented in the form of a performance curve for each type of fuse.

Standards define two classes of fuse:
• Those intended for domestic installations, manufactured in the form of a cartridge for rated currents up to 100 A and designated type gG in IEC 60269-1 and 3

• Those for industrial use, with cartridge types designated gG (general use); and Gm and aM (for motor-circuits) in IEC 60269-1 and 2
The first letter indicates the breaking range:
• “g” fuse-links (full-range breaking-capacity fuse-link)
• “a” fuse-links (partial-range breaking-capacity fuse-link)
The second letter indicates the utilization category; this letter defines with accuracy the time-current characteristics, conventional times and currents, gates.
For example
“gG” indicates fuse-links with a full-range breaking capacity for general application
“gM” indicates fuse-links with a full-range breaking capacity for the protection of motor circuits
“aM” indicates fuse-links with a partial range breaking capacity for the protection of motor circuits
The main differences between domestic and industrial fuses are the nominal voltage and current levels (which require much larger physical dimensions) and their fault-current breaking capabilities.

3) Circuit Breakers

A circuit breaker in equipment of Switch Gear is an equipment which can open or close a circuit under all conditions viz. no load, full load and fault conditions. It is so designed that it can be operated manually (or by remote control) under normal conditions and automatically under fault conditions. For the latter operation, a relay circuit is used with a circuit breaker.

Types of Low Voltage Circuit Breakers:

i) Miniature Circuit Breaker
ii) Moulded Case Circuit Breaker
iii) Residual Current Circuit Breaker

Types of Circuit Breakers w.r.t Arc Quenching Medium

i) Vacuum Circuit Breaker
ii) SF6 Circuit Breaker
iii) Oil Circuit Breaker
iv) Air Blast Circuit Breaker

4) Protective Relays

Protective relays are vital parts in Equipment of Switch Gear
A relay is a device which detects the fault and supplies information to the breaker for circuit interruption.
The function of a protective relay is to initiate a signal to circuit breakers for disconnecting the elements of the power system when it develops a fault.
When a fault occurs the relay, contacts are closed and the trip coil of the circuit breaker is energized to open the contacts of the circuit breaker.
There have been rapid developments in relaying technology during the last two decades. The most important advancement has been due to the advent of computer technology which has helped in the development of numerical relays.

Relays use in Switch Gear
1. Earth Fault and Over current relay
2. Power Factor Controller Relay
3. Transformer Status Relay
4. Protection System Relay
5. Feeder Protection Relay
6. Transformer Protection Relay
7. Earth Fault Relay
8. DC Supervision Relay

➢ Fundamental Requirements of Protective Relaying

The principal function of protective relaying is to cause the prompt removal front service of any element of the power system when it starts to operate in an abnormal manner or interfere with the effective operation of the rest of the system. In order that protective relay system may perform this function satisfactorily, it should have the following qualities:

• Selectivity

• Speed

• Sensitivity

• Reliability

• Simplicity

• Economy

1) The prompt removal of the component which is behaving abnormally by closing the trip circuit of the circuit breaker or to sound an alarm.

2) Disconnect the abnormally operating part so as to avoid the damage or interference within the effective operation of the rest of the system.

3) Prevent the subsequent faults by disconnecting the abnormally operating part.

4) Disconnect the faulty part as quickly as possible so as to minimize the damage to the faulty part itself. For example, if there is a winding fault in a machine and if it persists for a long time then there is a possibility of the damage of the entire winding. As against this, if it is disconnected quickly then only a few coils may get damaged instead of the entire winding.

5) Restrict the spreading of the effect of the fault causing the least interference to the rest of the healthy system. Thus, by disconnecting the faulty part, the fault effects get localized.

6) To improve system performance, system reliability, system stability, and service continuity. The faults cannot be completely avoided but can be minimized. Thus, the protective relaying plays an important role in sensing the faults, minimizing the effects of faults and minimizing the damage due to the faults.

7) Instrument Transformers

Instrument transformers (current transformer and voltage transformer) are used in switch gear installations for the measurement of electrical parameters for protection and metering purposes. An instrument transformer in which the secondary current is substantially proportional to the primary current and differs in phase from it by approximately zero degrees is called a current transformer (CT). A voltage transformer (VT) is an instrument transformer in which the secondary voltage is substantially proportional to the primary voltage and differs in phase from it by approximately zero degrees.

8) Magnetic Contractor

The magnetic contractor in equipment of switch gear is a solenoid-operated switching device which is generally held closed by (a reduced) current through the closing solenoid (although various mechanically-latched types exist for specific duties). Contractors are designed to carry out numerous close/open cycles and are commonly controlled remotely by on-off push buttons.

9) Discontractor

A contractor equipped with a thermal-type relay for protection against overloading defines a “discontractor”. Discontractors are used extensively for remote push-button control of lighting circuits, etc., and may also be considered as an essential element in a motor controller.

The discontractor is not the equivalent of a circuit-breaker, since its short-circuit current breaking capability is limited to 8 or 10 In. For short-circuit protection therefore, it is necessary to include either fuses or a circuit-breaker in series with, and upstream of, the discontractor contacts.

What is Switch Gear? And its main Function in Electrical System

November 1, 2021 by Opal Isaac Posted in Electrician Services

Switch Gear:

The apparatus used for controlling, regulating and switching on or off the electrical circuit in the electrical power system is known as switch gear. It also includes the combination of switching devices with associated control, measuring, protecting and regulating equipment. The switch gear devices and their assemblies are used in connection with the generation, transmission, distribution, and conversion of electrical energy. We all are familiar with low voltage switches and re-wireable fuses in our homes. Switches are used for opening and closing an electric circuit while fuses are used for over-current and short circuit protection. In such a way, every electrical device wants a switching and a protecting device. Various forms of switching and protective devices have been developed. Thus, switch gear can be taken as a general term covering a wide range of equipment concerned with the switching, protection, and control of various electrical equipment.

The main functions of switch gear are,

:• Electrical protection
• Electrical isolation of sections of an installation
• Local or remote switching

• Electrical protection in Switch Gear:

The aim is to avoid or to limit the destructive or dangerous consequences of excessive (short circuit) currents, or those due to overloading and insulation failure, and to separate the defective circuit from the rest of the installation. A distinction is made between the protection of:

• The elements of the installation (cables, wires, switch gear…)

• Persons and animals

• Equipment and appliances supplied from the installation

The protection of circuits

• Against overload; a condition of excessive current being drawn from a healthy (unfaulted) installation.

• Against short-circuit currents due to complete failure of insulation between conductors of different phases or (in TN systems) between a phase and neutral (or PE) conductor.
Protection in these cases is provided either by fuses or circuit-breaker, in the distribution board at the origin of the final circuit (i.e. the circuit to which the load is connected).

The protection of persons

• Against insulation failures. According to the system of earthing for the installation (TN, TT or IT) the protection will be provided by fuses or circuit-breakers, residual current devices, and/or permanent monitoring of the insulation resistance of the installation to earth.

The protection of electric motors

• Against overheating, due, for example, to long term overloading, stalled rotor, single-phasing, etc. Thermal relays, specially designed to match the particular characteristics of motors are used.
Such relays may, if required, also protect the motor-circuit cable against overload. Short-circuit protection is provided either by type aM fuses or by a circuit-breaker from which the thermal (overload) protective element has been removed, or otherwise made inoperative.

• Isolation

The aim of isolation is to separate a circuit or apparatus (such as a motor, etc.) from the remainder of a system which is energized, in order that personnel may carry out work on the isolated part in perfect safety.
An isolating device must fulfill the following requirements:

• All poles of a circuit, including the neutral (except where the neutral is a PEN conductor) must open. • It must be provided with a locking system in open position with a key (e.g. by means of a padlock) in order to avoid an unauthorized reclosure by inadvertence

• It must comply with a recognized national or international standard (e.g. IEC 60947-3) concerning clearance between contacts, creepage distances, over voltage withstand capability, etc.

• Switching

In broad terms “control” signifies any facility for safely modifying a load-carrying power system at all levels of an installation. The operation of switchgear is an important part of power-system control.
Functional control
This control relates to all switching operations in normal service conditions for energizing or de-energizing a part of a system or installation, or an individual piece of equipment, item of plant, etc.
Switch gear intended for such duty must be installed at least:

• At the origin of any installation

• At the final load circuit or circuits (one switch may control several loads)

Emergency switching – emergency stop
An emergency switching is intended to de-energize a live circuit which is, or could become, dangerous (electric shock or fire). An emergency stop is intended to halt a movement which has become dangerous.

In the two cases:

• The emergency control device or its means of operation (local or at remote location(s)) such as a large red mushroom-headed emergency-stop push button must be recognizable and readily accessible, in proximity to any position at which danger could arise or be seen.

• A single action must result in a complete switching-off of all live conductors

• A “break glass” emergency switching initiation device is authorized, but in unmanned installations the re-energizing of the circuit can only be achieved by means of a key held by an authorized person.
It should be noted that in certain cases, an emergency system of braking, may require that the auxiliary supply to the braking-system circuits be maintained until final stoppage of the machinery.

Switching-off for mechanical maintenance work

This operation assures the stopping of a machine and its impossibility to be inadvertent restarted while mechanical maintenance work is being carried out on the driven machinery. The shutdown is generally carried out at the functional switching device, with the use of a suitable safety lock and warning notice at the switch mechanism.

Solar Panels annd Difference Between Monocrystalline and Polycrystalline

November 1, 2021 by Opal Isaac Posted in Electrician Services

Photovoltaic solar panels absorb sunlight as a source of energy to generate direct current electricity. A photovoltaic (PV) module is a packaged, connected assembly of photovoltaic solar cells available in different voltages and wattages.

Photovoltaic modules constitute the photovoltaic array of a photovoltaic system that generates and supplies solar electricity in commercial and residential applications. Difference Between Monocrystalline and Polycrystalline Solar Panels are given below with advantages and advantages of both types.

Mono-crystalline solar panels:

The mono-crystalline solar panels cells are also known as single crystalline cells. They are incredibly easy to identify because they are a dark black in colour.

Mono-crystalline cells are made from an incredibly pure form of silicon, which makes them the most efficient material for the conversion of sunlight into energy.

Additionally, mono-crystalline cells are also the most space-efficient form of silicon solar cell. They also have the advantage of being the ones that last the longest out of all the silicon-based solar cells.

In fact, many manufacturers will offer warranties of up to 25 years on this type of system – a warranty that lasts half of their expected life. However, while these systems are superior, they do come at quite a hefty price.

Mono-crystalline cells are the most expensive option out of all of the silicon solar cell types, mostly because the four-sided cutting system results in a large amount of waste. Poly-crystalline acts as a cheaper alternative.

➢ Advantages of Mono-crystalline solar Cell:

Monocrystalline solar panels have the highest efficiency rates since they are made out of the highest-grade silicon.The efficiency rates of mono-crystalline solar panels are typically 15-20%. Sun Power produces the highest efficiency solar panels on the U.S. market today. Their E20 series provide panel conversion efficiencies of up to 20.1%. Update (April, 2013): Sun Power has now released the X-series at a record-breaking efficiency of 21.5%.Monocrystalline silicon solar panels are space-efficient. Since these solar panels yield the highest power outputs, they also require the least amount of space compared to any other types.Mono-crystalline solar panel produce up to four times the amount of electricity as thin-film solar panels.Mono-crystalline solar panel live the longest. Most solar panel manufacturers put a 25-year warranty on their mono-crystalline solar panel.Tend to perform better than similarly rated poly-crystalline solar panel at low-light conditions.

➢ Disadvantages of Mono-crystalline solar Cell:

Mono-crystalline solar panels are the most expensive.From a financial standpoint, a solar panel that is made of poly-crystalline silicon (and in some cases thin-film) can be a better choice for some homeowners.If the solar panel is partially covered with shade, dirt or snow, the entire circuit can break down. Consider getting micro-inverters instead of central string inverters if you think coverage will be a problem. Micro-inverters will make sure that not the entire solar array is affected by shading issues with only one of the solar panels. The Czochralski process is used to produce mono-crystalline silicon. It results in large cylindrical ingots. Four sides are cut out of the ingots to make silicon wafers. A significant amount of the original silicon ends up as waste.Monocrystalline solar panels tend to be more efficient in warm weather.Performance suffers as temperature goes up, but less so than polycrystalline solar panel. For most home owners temperature is not a concern.

Poly-crystalline silicon Solar Panels:

The polycrystalline solar cells are also known as polysilicon and multi-silicon cells. They were the first solar cells to be developed when the industry started in the 1980s.

Most interestingly, polycrystalline cells do not undergo the same cutting process as the monocrystalline cells. Instead, the silicon is melted and then poured into a square mould. This is what creates the specific shape of the polycrystalline.

One of the benefits of this process is that the solar cells become much more affordable. This is because hardly any silicon is wasted during the manufacturing process.

However, they are less efficient than monocrystalline solar cells, and also require a lot more space. This is due to the fact that they have lower levels of purity than the single crystalline cell models.

Poly-crystalline also has a lower tolerance for heat than mono-crystalline. This means that they are unable to function as efficiently in high temperatures. This can be a massive disadvantage in areas with hot climates.

➢ Advantages of Poly-crystalline silicon Solar Panels:

The process used to make poly-crystalline silicon is simpler and cost less. The amount of waste silicon is less compared to mono-crystalline.Poly-crystalline solar panel tend to have slightly lower heat tolerance than mono-crystalline solar panel. This technically means that they perform slightly worse than mono-crystalline solar panels in high temperatures.Heat can affect the performance of solar panel and shorten their lifespans. However, this effect is minor, and most homeowners do not need to take it into account.

➢ Disadvantages of Poly-crystalline silicon Solar Panels:

The efficiency of poly-crystalline-based solar panel is typically 13-16%. Because of lower silicon purity, poly-crystalline solar panels are not quite as efficient as mono-crystalline solar panel.Lower space-efficiency. You generally need to cover a larger surface to output the same electrical power as you would with a solar panel made of mono-crystalline silicon. However, this does not mean every mono-crystalline solar panel perform better than those based on poly-crystalline silicon.Mono-crystalline and thin-film solar panels tend to be more aesthetically pleasing since they have a more uniform look compared to the speckled blue color of poly-crystalline silicon.

Opal Isaac

countryelectric.biz

Electromechanical induction type Energy meter and Its working Principle

November 1, 2021 by Opal Isaac Posted in Electrician News

Electromechanical induction type Energy meter

An electricity meterelectric meterelectrical meter, or energy meter is a device that measures the amount of electric energy consumed by a residence, a business, or an electrically powered device.

It is the popularly known and most common type of age old watt hour meter. It consists of rotating aluminum disc mounted on a spindle between two electro-magnets. Speed of rotation of disc is proportional to the power and this power is integrated by the use of counter mechanism and gear trains in. It comprises of two silicon steel laminated electromagnets i.e., series and shunt magnets.

Series magnet carries a coil which is of few turns of thick wire connected in series with line whereas shunt magnet carries coil with many turns of thin wire connected across the supply.

Breaking magnet is a permanent magnet which applies the force opposite to normal disc rotation to move that disc at balanced position and to stop the disc while power is off.

Working Principle:

The working of single phase induction type energy meters are based on two main fundamentals:

i. Rotation of aluminum disk.

ii. Arrangement of counting and displaying the amount of energy consumed.

Rotation of an Aluminum Disk:

The rotation of metallic disk is operated by two coils. Both the coils are arranged in such way that one coil produces a magnetic field in proportion to voltage and the other coil creates a magnetic field proportion to current. The field produced by voltage coil is delayed by 90° so that eddy current is induced in the disk. The force exerted on the disk by the two fields is proportional to the product of the immediate current and voltage in the coils.

As a result of it, a lite weight aluminum disk rotates in an air gap. But there is a need to stop a disk when there is no power supply. A permanent magnet works as a brake which opposes the rotation of the disk and balances the speed of rotation with respect to power consumption.

Arrangement of Counting and Displaying the Energy Consumed:

In this system, the rotation of the floating disk has been counted and then displayed on the meter window. The aluminum disk is connected to a spindle which has a gear. This gear drives the register and the revolution of the disk has been counted and displayed on the register which has series of dials and each dial represent a single digit. There is a small display window in the front of the meter which displays the reading of energy consumed with the help of dials. There is a copper shading ring at the central limb of the shunt magnet. To make the phase angle between flux produced by shunt magnet and supply voltage about 900, small adjustments in the place of the ring is required.

Read for more about Energy Meters