Increasing the number of primary turns can decrease the turn‟s ratio. A current transformer with
a 300 to 5 turn‟s ratio can be changed to a 150 to 5 turn‟s ratio by passing the primary twice
a 300 to 5 turn‟s ratio can be changed to a 150 to 5 turn‟s ratio by passing the primary twice
through the window. Also
through the window. Also
the turn‟s ratio can be eitthe turn‟s ratio can be eit
her increased or decreased by wrapping wireher increased or decreased by wrapping wire from the secondary through the window of the current transformer.from the secondary through the window of the current transformer.
2.4.2. Core
2.4.2. Core Balance Current TransformerBalance Current Transformer
The Core Balance Current Transformer is a current transformer is used for earth fault protection The Core Balance Current Transformer is a current transformer is used for earth fault protection in grounded three phase systems. It is also known as the zero-sequence current transformer. Each in grounded three phase systems. It is also known as the zero-sequence current transformer. Each phase
phase conductor conductor and and neutral neutral should should pass pass through through the the core core balance balance current current transformer. transformer. It It isis essential that each conductor passes through the device in the same direction. essential that each conductor passes through the device in the same direction.
Figure 2.4.1.3 - CT connection Figure 2.4.1.3 - CT connection
Figure 2.4.2 - Core Balance Cu
Working principle of Core Balance CTWorking principle of Core Balance CT
The net resultant flux being zero does not induce any current in the secondary of the transformer. The net resultant flux being zero does not induce any current in the secondary of the transformer. Thus the secondary current of the core balance current transformer when all the three phases are Thus the secondary current of the core balance current transformer when all the three phases are healthy is zero. When an earth fault occurs in one of the phases, the zero-sequence fault current healthy is zero. When an earth fault occurs in one of the phases, the zero-sequence fault current which flows is not cancelled by the flux of the other two phases and hence induces a current in which flows is not cancelled by the flux of the other two phases and hence induces a current in the secondary. The core balance current transformer can be connected to an earth fault relay the secondary. The core balance current transformer can be connected to an earth fault relay which can be used to generate the tripping signal.
which can be used to generate the tripping signal.
2.4.3. Indicator
2.4.3. Indicator
Indicators are used to get information about states of equipment such as ON (Green), OFF (red), Indicators are used to get information about states of equipment such as ON (Green), OFF (red), TRIP (Orange).
TRIP (Orange). Indicators are available in read yellow blue and orange and 12V to 230V. Indicators are available in read yellow blue and orange and 12V to 230V.
2.4.4. Ammeter
2.4.4. Ammeter
An ammeter is a
An ammeter is a measuring instrument measuring instrument used to measure theused to measure the electric current electric current in in aa circuit. circuit. Current Current transformers and ammeters are used together as a matched pair in which the design of the current transformers and ammeters are used together as a matched pair in which the design of the current transformer is such as to provide a maximum secondary current corresponding to a full-scale transformer is such as to provide a maximum secondary current corresponding to a full-scale deflection on the ammeter. For most current transformers the primary and secondary currents are deflection on the ammeter. For most current transformers the primary and secondary currents are expressed as a ratio such as rated
expressed as a ratio such as rated current : 5A.current : 5A.
2.4.4.1. Connecting process of an Ammeter 2.4.4.1. Connecting process of an Ammeter
I was able practice connecting process of the I was able practice connecting process of the Ammeter in to the panels.Ammeter in to the panels.
In 3 phase system, 3 position selector switch was In 3 phase system, 3 position selector switch was used to select the 3 phases used to select the 3 phases R, Y or B.R, Y or B.
CTs were connected in to the selector switch.CTs were connected in to the selector switch.
The selector switch was connected with the Ammeter A1 and A2.The selector switch was connected with the Ammeter A1 and A2.
Figure 2.4.3
2.4.5. Voltmeter
2.4.5. Voltmeter
A voltmeter is an instrument used for measuring
A voltmeter is an instrument used for measuring electrical potentialelectrical potential difference between twodifference between two points in an
points in an electric circuit. Analog electric circuit. Analog voltmeters move a voltmeters move a pointer across a pointer across a scale in scale in proportion to theproportion to the voltage of the circuit. The voltmeter selector switch is used to select the two phases or phase- voltage of the circuit. The voltmeter selector switch is used to select the two phases or phase- neutral in 3 phase system.
neutral in 3 phase system.
2.4.6. KWH Meter
2.4.6. KWH Meter (Energy meter)(Energy meter)
KWH Meter is used to measure the kW power. Mainly we use two types of KWh meters. Those KWH Meter is used to measure the kW power. Mainly we use two types of KWh meters. Those are single-phase kWh meters and three phase kWh meters. These three phase & single-phase are single-phase kWh meters and three phase kWh meters. These three phase & single-phase meters are can be dividing again like this C/T type and direct type. Mostly we use C/T type meters are can be dividing again like this C/T type and direct type. Mostly we use C/T type energy meters. In some panels, used di
energy meters. In some panels, used digital KWH meters.gital KWH meters.
2.4.7. Digital Power Analyzer
2.4.7. Digital Power Analyzer
Power analyzers accurately measure electrical power characteristics of the system. Power Power analyzers accurately measure electrical power characteristics of the system. Power analyzers, also called power meters or watt meters, provide precise measurements of power analyzers, also called power meters or watt meters, provide precise measurements of power supply system. This is useful for getting to power consumption and many more values of the supply system. This is useful for getting to power consumption and many more values of the system.
system.
I was able to refer metering performed of Schneider PM 700 digital analyzer, I was able to refer metering performed of Schneider PM 700 digital analyzer,
Current - (per phase/ neutral) min/max Current demand: presentCurrent - (per phase/ neutral) min/max Current demand: present
Voltage - (line-line/ line-neutral) per phase, min/maxVoltage - (line-line/ line-neutral) per phase, min/max
Power: - real (kW), reactive (kvar), apparent (kVA), per-phase, totalPower: - real (kW), reactive (kvar), apparent (kVA), per-phase, total
Energy: - real (kWh), reactive (kvarh), apparent (kVAh)Energy: - real (kWh), reactive (kvarh), apparent (kVAh)
Signed power factor:- Signed power factor:- total, min/maxtotal, min/max
Frequency: - present, min/maxFrequency: - present, min/max
Figure 2.4.4
2.5. Switching Devises Used in the Panels
2.5. Switching Devises Used in the Panels
2.5.1 Relay
2.5.1 Relay
A relay is a switching device. Relays are used where it is necessary to control a circuit by a low- A relay is a switching device. Relays are used where it is necessary to control a circuit by a low- power signal
power signal with complete with complete electrical isolation electrical isolation between control between control and conand controlled circuits trolled circuits or whereor where several circuits must be controlled by one signal.
several circuits must be controlled by one signal.
Relay consists with coil, normally open and normally closed contact points. When current starts Relay consists with coil, normally open and normally closed contact points. When current starts flowing through the control coil, the electromagnet starts energizing and contact points are flowing through the control coil, the electromagnet starts energizing and contact points are changed their position.
changed their position.
Coil voltage can be 12V to 230V AC or DC. Also contact current rating is important factor. Coil voltage can be 12V to 230V AC or DC. Also contact current rating is important factor. According to the contact pin arrangement, relays are categorized as 8 pins, 11 pins, 14 pins and According to the contact pin arrangement, relays are categorized as 8 pins, 11 pins, 14 pins and etc. relay is fixed with its base.
etc. relay is fixed with its base.
2.5.2. Contactor
2.5.2. Contactor
I was able to identify the contactor construction and usages, because contactor was used in every I was able to identify the contactor construction and usages, because contactor was used in every motor control panel. It was used for the high power application switching on power circuit. Also motor control panel. It was used for the high power application switching on power circuit. Also I connected timers, auxiliary contact points (side and top), timers and mechanical interlock to the I connected timers, auxiliary contact points (side and top), timers and mechanical interlock to the