Different types of drive redundancy and their use cases
Redundancy in medium voltage (MV) drives is a critical design consideration aimed at enhancing the reliability and availability of motor-driven systems.
Drives with some types of redundancy are used in applications where high availability is requested. The reasons for this lay in the high cost for production downtime, enhanced safety, operation flexibility and cost efficiency. A vessel for example can not be left in the ocean without maneuverability when the propulsion fails. The redundancy, if semi or full, ensures partial power operation in any case and therefore extends the system failure capability. It is used in industrial applications, where downtime can lead to significant financial losses and operational disruptions and ensuring continuous operation is para
mount, hence marine applications like cruise ships, ferries, applications with dynamic positioning such as drill ships, mining applications such as hoists and in the Oil and Gas industry.
There are several approaches to achieving redundancy in MV Drives:
With component redundancy an uninterrupted operation in power modules, control modules and cooling modules is ensured. To create a redundancy in the weakest components of the drive gives you back a super tool. In case of a water cooled drive, the cooling cabinet contains redundant pumps to prevent a failure of the cooling system. In case of air cooled drives, redundant fans are procurable.
Some applications need a redundant auxiliary power supply to ensure a safe shut down of the drive in a failure case. System redundancy involves having a complete backup drive system, which can be switched to in case the primary system fails. This can be implemented using manual or automated transfer switches. With the parallel redundancy multiple drives operate in parallel to share the load. If one fails, the remaining drives continue to operate.
Single-motor drive configurations
Single motor drives are typically used in applications which need high power, independent operating and decentralized positioned drives. The configuration is based on two levels – basic and parallel operation.
For the basic version, the drive contains the basics of cabinets, such as a rectifier from the transformer input of the customer, an inverter that powers the motor, cooling unit, control unit and in case of a synchronous motor an excitation unit.
The parallel configuration is mainly used for high- performance drives. They contain a parallel connection of the inverter units, which power the motor, to arrive at a higher power. Usually also the active rectifier unit at the input is doubled.
Semi- redundancy
For the semi- redundant application mainly two types are available. As a first type we have a single motor drive mirrored, but built as one drive. This means that every cabinet is doubled and the construction is mirrored. The input, the power output, the cooling and the control. The second part is separated by an isolation unit.
The second type of semi-redundant MV Drives does not contain an isolation unit and only a single control and cooling unit. Only the power cabinets are doubled, and the mirroring is not required. A variable speed motor with double stator and a YY0 or YY30 configuration can be operated in two power modi: In the full power modus the drive operates both power units in parallel. For the half power modus only one power unit is activated. The transition between the two modi is not smooth, hence creates bumps.
Full redundancy
For the full redundant application two complete single motor drives with the same configuration are in stalled in parallel. Both contain a special cabinet for the communication with each other. In the (N+1) redundancy, the system requires one additional converter than needed by the system. It is only turned on occasionally to ensure that all functions are still available or when one of the main converters fail. In the hot standby configuration, the redundant converter is kept in a ready-to-operate state, allowing an immediate switchover in case of a failure.
The two drives power a double-stator motor with YY30 configuration. Again, the two modi full power and half power are available, although with full redundancy half power means, that only one drive is operating the motor.
Redundant auxiliary power supply
This option provides a solution with two uninterruptible power supplies without internal communication. Both feed an unknown percentage of the total power. If one fails, the other takes over 100%. The supervision is executed by voltage supervision relais. The UPS generally is provided by the customer with the redundancy in his scope. An engineered option is purchasable, with the redundand UPS within the drive. Redundant UPS enable a controlled shut down of the drive in case of a failure. The pumps in the water cooling unit have their own power supply and will be lost if the drives needs to be turned off.
Check the entire series on availability and reliability HERE.
Redundant cooling system
To improve system availability, it is possible to equip the drive with an additional redundantly operating cooling mechanism, such as a redundant pump (n+1) in a water cooled drive or a redundant fan (n+1) in an air cooled drive. The control mechanism behind is the same, no matter which cooling system is chosen. If a failure of the running cooling circuit is detected, the redundant one is activated by the converter control system without the drive being interrupted. This can prevent production down times, as replace ment can be scheduled for a suitable down time. The common case for the water cooling unit involves two redundant pumps where one is running at a higher amount of time than the other to prevent a
necessary change at the same time. For the air cooled version, usually more than 2 are installed and run ning with one redundant. In the second case, all cooling mediums are running with a lower power. If a medium fails, the other cover it by running with more power. This application leads to less wear and tear and also less noise.
This article was authored by Fiammetta Zanazzi from INP Schweiz AG.
Sources:
[1] ACS6080 industrial drive – a technical catalog, ABB ACS6080 catalog link
[2] S. Mouty, A. Rauber, Improving VSD System Availability by using Fully Redundant Power Converters, PCIC Europe 2022
[3] A. F. Cupertino, J. V. M. Farias, H. A. Pereira, P.R. M. Junior, M.M. Stopa and J. T. Resende, Redundancy and Derating Strategies for Modular Multilevel Converter for an Electric Drive, GESEP 2019, link
[4] Medium voltage drives for reliability and safe operation at sea, ABB marine brochure, link to download
[5] Sinamics GM150 and SM150 technical catalog, catalog link
0 Comments