Medium Voltage Technology

Switchgear

The IGEL® Electric company develops, produces and sells medium voltage switchgear systems of a new generation. In this context the two switchgear systems MV-C and MV-CS present the “external frame” for the installed switchgear technique. The electrical relevant components are subject to a strict quality control and will be selected according to the requested demands of each order. Not only the IGEL® parts are subject to this quality control but also all standard components of the switchgear technique.

A basic advantage is the independence of the design in respect of the manufacturers. All switchgear systems have been developed for all common switchgear devices. Due to this productneutral platform IGEL® Electric will be in the position to always select the most convenient switchgear device. On the one hand the selection criteria may be based on technical aspects like e.g. switching frequency, short circuit withstand or class. On the other hand our experiences with special product lines as well as the price play a decisive role. Additionally, we are able to meet the requirements of our customers by installing the requested switchgear devices, without being dependent on the switchgear of a single manufacturer. This also considerably reduces the spare part storage costs of our customers.

In the following the key requirements of the most important switchgear devices and components are listed.

According to Standard: IED 62 271-100, VDE 0671-100

Main switches are principally used in the field of energy distribution. The main selection criteria are the switching performance as well as the short circuit power. For larger drive systems the main switches will be installed in the line- and bypass. In this special case the switching frequency is an additional selection criterion.

According to standard: IEC 62 271-102; VDE 0671-102

Earth switches have the function to first of all protect the personnel which is working on the switchgear or the connected switchgear parts. Depending on their configuration they should guarantee that there is no voltage in the panels.

According to standard: IEC 60 282; VDE 0670-4

Fuses are installed for switchgear and user protection. In the opposite to the circuit breaker the fuses limit the short-circuit current to a considerably lower maximum current value. This enables that some parts of the switchgear may be according to a lower short circuit as well as internal arc classification since they will be protected by the fuses. From the technical point of view fuses are only applicable to a certain size. The performance limits may be extended in case of parallel switchgears.

According to standard: IEC 60 265-1; VDE 0670-301

In a medium voltage switchgear system the load break switches will principally be used as control elements. By the load break switches certain sections of the switchgear system may be connected or disconnected.

According to standard: IEC 60 071; VDE 0111
According to standard: IEC 60 044-2; VDE 0414-2

Voltage transformer will nearly be installed in every switchgear system. Depending on the protection concept the voltage level is observed directly, will be switched off in certain situations or will only be indicated and passed on to the next higher-ranking protection installation.

According to standard: IEC 60 044-1, VDE 0414-1

Current transformers form the basics of each protection system. Depending on the requested performances we use devices with the corresponding precision and saturation class. Especially in drive technology we often use double core transformer since besides the protection function the transformer also is providing the control value for the drive technology.

According to standard: IEC 60 470; VDE 60 871-1

All contactors used in the medium voltage area are realized using the vacuum technique. These contactors provide a maximum of switching possibilities and additionally may withstand but not switch a certain short circuit current. Therefore, we have to install short circuit limiting elements upstream of the contactors. In case the net has high short circuit power the fuses have to be positioned upstream or circuit breakers have to be installed.

According to standard: IEC 60 871-1

Capacitors are used to improve the power factor. Because of the extensive distribution of power electronics the harmonics should always be considered when deciding for a product. In case of doubt the capacitors have to be protected against high frequency disturbance by installing upstream connected chokes. For soft starter applications in general the careful selection of capacitors is granting the availability of the switchgear.

Definition of terms

Definition: The incoming field is referred to all fields which are used for the energy feeding of the switchgear system. In this case the source of supply voltage (transformer, outgoing field, generator) is not decisive.

Applications: The incoming fields may be used for energy distribution as well as for drive technology systems. They have to connect the supply voltage with the busbar system of the switchgear system by installing the corresponding components.

Design: In general incoming fields will be equipped with withdrawable cuircut breakers. In combination with the corresponding protection device they guarantee the protection of the switchgear system. Furthermore, the disconnector/fuse combination is installed very often.

Features: Since the incoming fields are directly connected to the external supply voltage which in most cases will be supplied from components outside the control room special features are requested. A special locking mechanism has to guarantee that neither a switching operation in the incoming field nor in the upstream connected supply field cause an undesirable status (e.g. short circuit).

Definition: The outgoing field is referred to all fields which form the outgoing of a system and are connected to another system or the end user.

Applications: The outgoing fields are switching and controlling the connected systems. They also dispose of protection functions like e.g. the motor or overcurrent protection relay.

Design: Depending on the demands of the connected system the corresponding components will be installed. In case of a low switching frequency (e.g. transformer) the outgoing field will be equipped with a circuit breaker or a main switch with fuses. For high switching frequencies (e.g. motor) vacuum contactors or a motor starting system has to be built in.

Features: For outgoing fields the personal protection is an important criterion. In order to guarantee safe works on connected components all outgoing cables are grounded. Additionally, a locking system is securing the outgoing field against unintentional reconnection.

Definition: Coupling fields are referred to all fields which are connecting two busbar systems (coupling).

Applications: Complexe switchgear systems e.g. redundant systems or switchgear systems with two incoming fields have to offer the possibility of different configurations. In this case the coupling fields serve as connecting or final controlling element.

Design: As switching component either disconnectors or circuit breakers are used.

Features: Like the incoming fields also the coupling fields may produce unwanted and critical switching statuses. Therefore, all switching components which are installed into the coupling fields have to be completely integrated into the locking system.

Definition: Soft starters are designed to provide a smooth and stepless acceleration of electrical asynchronous motors by using power electronic components (Thyristors).

Applications: Applications which need a motor start to be grid protecting (reduced starting current) and/or mechanic protecting (reduced starting torque).

Design: A soft starter always is with built in power electronic the so called power stacks. In the medium voltage section a bypass contactor as well as main switch are prescribed. Often additional fuses, earth disconector as well as motor protection relays are installed into a soft starter.

Features: During the motor start-up the power electronic is producing heat. This has to be considered for the switchgear design. The signal transmission by using fibre optics is granting a strict separation between low voltage and medium voltage section.

Definition: Start-up units which start the motor by using common switching components (vacuum contactor or power switch).

Applications: Applications without any critical phase during start up in respect of loading the grid and torque peaks.

Design: Switching component in form of a vacuum contactor or circuit breaker. Current transformer and motor protection relay. Vacuum contactors are often used in combination with the corresponding fuses.

Features: For outgoing fields the personal protection is an important criterion. In order to guarantee safe works on connected components all outgoing cables are grounded. Additionally, a locking system is securing the outgoing field against unintentional reconnection.

Definition: Autotransformers are motor start-up units using transformers tapping on the secondary part and supplying the motor with the corresponding ramped voltage.

Applications: Applications which need a reduced current during starting phase.

Design: Special transformer in the Korndorfer transition principle using specific switching components and supplying the motor with the corresponding ramped voltage. Very often protection components like fuses, current transformers and motor protection relays are installed.

Features: The high weight as well as the dimensions of this special transformer make it necessary to supply the starting transformer field in extended design.

Different types of starting