Functions of the substation with MV metering: Difference between revisions

Latest revision as of 09:49, 22 June 2022

Connection to the MV network

Connection to the MV network can be made:

By a single service cable or overhead line,
By dual parallel feeders via two mechanically interlocked load-break switches
Via a ring main unit including two load-break switches.

MV/LV Transformers and internal MV distribution

As mentioned for substation with LV metering, only oil-immersed and dry type cast-resin transformers are allowed with the same rules of installation.

When the installation includes several MV/LV transformers and/or secondary MV/ LV substations an internal MV distribution network is required.

According to the required level of availability, the MV supplies to the transformers and the secondary substations may be made,

By simple radial feeders connected directly to the transformers or to the secondary substations
By one or several rings including the secondary MV/LV substations Fig. B10
By duplicate feeders supplying the secondary MV/LV substations.

For the two latter solutions the MV switchboard located in each secondary substation includes two load break switch functional units for the connection of the substation to the internal MV distribution and one transformer protection unit, for each transformer installed in the substation.

The level of availability can be increased by using two transformers operating in parallel or arranged in dual configuration with an automatic change over system.

It is not recommended to use MV/LV transformers above 2500 kVA due to:

The high level of the short circuit current generated on the main LV switchboard.
The number of LV cable required for the connection of the transformer to the LV switchboard.

Metering

The characteristics and the location of the VT’s and CT’s dedicated to the metering shall comply with the utility requirements.

The VT’s and CT’s are generally installed in the MV switchboard. A dedicated functional unit is in most of the cases required for the voltage transformers while the current transformers may be contained in the functional unit housing the circuit breaker ensuring the general protection of the substation.

The panel that contains the meters shall be accessible by the utility at any time.

Local emergency generators

Emergency standby generators are intended to maintain the power supply to the essential loads in the event of failure of the utility power supply.

According to the energy needs an installation may contains one or several emergency generators.

The generators can be connected:

At MV level to the MV main substation (see Fig. B33).The generator(s) may be sized either for the supply of the whole installation or for a part only. In this case a load shedding system must be associated to the generator(s).
At LV level on one or several LV switchboards requiring an emergency supply. At each location, the loads requiring an emergency supply may be grouped on a dedicated LV busbar supplied by a local generator (see Fig. B31 in Local emergency generators at LV level).

Fig. B33 – Connection of emergency generators at MV level

Capacitors

Capacitors are intended to maintain the power factor of the installation at the contractual value specified by the utility. The capacitor banks can be fixed or adjustable by means of steps. They can be connected:

At MV level to the main MV substation
At LV level on LV switchboards.

LV main switchboard

Every MV/LV transformer is connected to a main LV switchboard complying with the same requirements listed for substation with LV metering.

Simplified electrical network diagram

The diagram Fig. B34 shows:

The different methods to connect a MV/LV substation to the utility supply:
- Spur network or single-line service
- Single line service with provision for future connection to a ring or to dual parallel feeders
- Dual parallel feeders
- Loop or ring-main service
General protection at MV level
MV metering functions
Protection of MV circuits
LV distribution switchboard

Compared with a substation with LV metering, a substation with MV metering includes in addition:

A MV Circuit breaker functional unit for the general protection of the substation
A MV metering functional unit
MV Functional units dedicated to the connection and the protection of:
- MV/LV transformers
- MV feeders supplying secondary substations
- MV capacitor banks
- Emergency generators

The general protection usually includes protection against phase to phase and phase to earth faults. The settings must be coordinated with the protections installed on the feeder of the primary substation supplying the installation.

Fig. B34 – Consumer substation with MV metering

@@ Line 1: / Line 1: @@
 {{Menu_Connection_to_the_MV_utility_distribution_network}}
-__TOC__
+== Connection to the MV network ==
-<br>
-{{Highlightbox|
+Connection to the MV network can be made:
-A consumer substation with MV metering is an electrical installation connected to a utility supply system at a nominal voltage of 1 kV - 35&nbsp;kV and generally includes a single MV/LV&nbsp;transformer which exceeds 1,250 kVA, or&nbsp;several smaller transformers.<br>The rated current of the MV switchgear does not normally exceed 400 A.
+* By a single service cable or overhead line,
-}}
+* By dual parallel feeders via two mechanically interlocked load-break switches
+* Via a ring main unit including two load-break switches.
-The different functions of the substation are:
+== MV/LV Transformers and internal MV distribution ==
-'''The substation'''<br>According to the complexity of the installation and the manner in which the load is divided, the substation:
+As mentioned for substation with LV metering, only oil-immersed and dry type cast-resin transformers are allowed with the same rules of installation.
-*Might include one room containing the MV switchboard and metering panel(s), together with the transformer(s) and low-voltage main distribution board(s),
+When the installation includes several MV/LV transformers and/or secondary MV/ LV substations an internal MV distribution network is required.
-*Or might supply one or more transformer rooms, which include local LV distribution boards, supplied at MV from switchgear in a main substation, similar to that described above.
-These substations may be installed, either:
+According to the required level of availability, the MV supplies to the transformers and the secondary substations may be made,
-*Inside a building, or&nbsp;
+* By simple radial feeders connected directly to the transformers or to the secondary substations
-*Outdoors in prefabricated housings.<br>
+* By one or several rings including the secondary MV/LV substations {{FigRef|B10}}
+* By duplicate feeders supplying the secondary MV/LV substations.
-'''Connection to the MV network'''<br>Connection at MV can be:
+For the two latter solutions the MV switchboard located in each secondary substation includes two load break switch functional units for the connection of the substation to the internal MV distribution and one transformer protection unit, for each transformer installed in the substation.
-*Either by a single service cable or overhead line, or
+The level of availability can be increased by using two transformers operating in parallel or arranged in dual configuration with an automatic change over system.
-*Via two mechanically interlocked load-break switches with two service cables from duplicate supply feeders, or
-*Via two load-break switches of a ring-main unit.<br>
-'''Metering'''<br>Before the installation project begins, the agreement of the power-supply utility regarding metering arrangements must be obtained.<br>A metering panel will be incorporated in the MV switchboard. Voltage transformers and current transformers, having the necessary metering accuracy, may be included in the main incoming circuit-breaker panel or (in the case of the voltage transformer) may be installed separately in the metering panel. <br>
+It is not recommended to use MV/LV transformers above 2500 kVA due to:
+* The high level of the short circuit current generated on the main LV switchboard.
+* The number of LV cable required for the connection of the transformer to the LV switchboard.
-'''Transformer rooms'''<br>If the installation includes a number of transformer rooms, MV supplies from the main substation may be by simple radial feeders connected directly to the transformers, or by duplicate feeders to each room, or again, by a ring-main, according to the degree of supply availability desired. In the two latter cases, 3-panel ring-main units will be required at each transformer room. <br>
+== Metering ==
-'''Local emergency generators'''<br>Emergency standby generators are intended to maintain a power supply to essential loads, in the event of failure of the power supply system. <br>
+The characteristics and the location of the VT’s and CT’s dedicated to the metering shall comply with the utility requirements.
-'''Capacitors'''<br>Capacitors will be installed, according to requirements:
+The VT’s and CT’s are generally installed in the MV switchboard. A dedicated functional unit is in most of the cases required for the voltage transformers while the current transformers may be contained in the functional unit housing the circuit breaker ensuring the general protection of the substation.
-*In stepped MV banks at the main substation, or
+The panel that contains the meters shall be accessible by the utility at any time.
-*At LV in transformer rooms.<br>
-'''Transformers'''<br>For additional supply-security reasons, transformers may be arranged for automatic changeover operation, or for parallel operation. <br>
+== Local emergency generators ==
-== One-line diagrams  ==
+Emergency standby generators are intended to maintain the power supply to the essential loads in the event of failure of the utility power supply.
-The diagrams shown in '''Figure B19 '''represent:
+According to the energy needs an installation may contains one or several emergency generators.
-*The different methods of MV service connection, which may be one of four types:
+The generators can be connected:
+* At MV level to the MV main substation (see {{FigRef|B33}}).The generator(s) may be sized either for the supply of the whole installation or for a part only. In this case a load shedding system must be associated to the generator(s).
+* At LV level on one or several LV switchboards requiring an emergency supply. At each location, the loads requiring an emergency supply may be grouped on a dedicated LV busbar supplied by a local generator (see {{FigRef|B31}} in [[Functions_of_a_substation_with_LV_metering#Local_emergency_generators|Local emergency generators at LV level]]).
-'''&nbsp; - '''Single-line service<br>&nbsp; '''- '''Single-line service (equipped for extension to form a ring main)<br>&nbsp; '''- '''Duplicate supply service<br>&nbsp; - Ring main service
+{{FigImage|DB422035_EN|svg|B33|Connection of emergency generators at MV level}}
-*General protection at MV, and MV metering functions
+== Capacitors ==
-*Protection of outgoing MV circuits
-*Protection of LV distribution circuits
-----
+Capacitors are intended to maintain the power factor of the installation at the contractual value specified by the utility. The capacitor banks can be fixed or adjustable by means of steps. They can be connected:
+* At MV level to the main MV substation
+* At LV level on LV switchboards.
-[[File:FigB19.jpg|none]]
+== LV main switchboard ==
-'''''Fig. B19: '''Consumer substation with MV metering''
-----
+Every MV/LV transformer is connected to a main LV switchboard complying with the same [[Functions_of_a_substation_with_LV_metering#LV_main_switchboard|requirements listed for substation with LV metering]].
-<br>
+== Simplified electrical network diagram ==
-[[ru:Функции подстанции с учетом на высоком напряжении]]
+The diagram {{FigRef|B34}} shows:
-[[zh:中压计量变电站的作用]]
+* The different methods to connect a MV/LV substation to the utility supply:
+**Spur network or single-line service
+**Single line service with provision for future connection to a ring or to dual parallel feeders
+**Dual parallel feeders
+**Loop or ring-main service
+* General protection at MV level
+* MV metering functions
+* Protection of MV circuits
+* LV distribution switchboard
+Compared with a substation with LV metering, a substation with MV metering includes in addition:
+* A MV Circuit breaker functional unit for the general protection of the substation
+* A MV metering functional unit
+* MV Functional units dedicated to the connection and the protection of:
+**MV/LV transformers
+**MV feeders supplying secondary substations
+**MV capacitor banks
+**Emergency generators
+The general protection usually includes protection against phase to phase and phase to earth faults. The settings must be coordinated with the protections installed on the feeder of the primary substation supplying the installation.
+{{FigImage|DB422036_EN|svg|B34|Consumer substation with MV metering}}

Functions of the substation with MV metering: Difference between revisions

Latest revision as of 09:49, 22 June 2022

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