PLCS & INDUSTRIAL PCS SUPPLEMENT FEATURE
GIVING MULTI-VOLTAGE capability to pump test station
A multi-voltage pump testing station, just delivered to one of the world’s leading pump manufacturers, has been built by SoftStart UK. Here, managing director Stuart Harvey explains more
T
he pump test station is based on a 400A, 11kV soft start fitted with special
electronic potential transformers that automatically identify the incoming voltage to assist with swift and accurate set-up for each test. A programmable logic controller (PLC) is used for overall control of the test station and holds a number of different test protocol in its memory. The design brief required that the test
station accepts 3.3kV, 5kV, 6.6kV, 10kV and 11kV incoming voltages from five different transformer feeders. This enables the station to test different voltage motors from 30A to 400A. “The smallest motor the station can test
is 155kW at 3.3kV,” explained Harvey. “The largest is 6.4MW at 11KV. So it has the capability to test some very large pumps, such as would be used on city wide water distribution networks, for major crop irrigation systems, flood defences and in oilfield installations.”
PROBLEM SOLVING Starting pumps of even the smallest sizes associated with the test station can raise several issues. There can be damaging mechanical shock loads transmitted through the pump and drive system - pressure pulses (often experienced as water hammer) can be sent reverberating around the pipe network, and harmonic disturbances can be induced into the electrical mains. “Larger pumps are usually installed with a soft start to get over these problems,” Harvey added. “So it is fitting that the test station is also based on a soft start.” A soft start is an electrical device used in
conjunction with electric motors, and as the name implies it functions to smooth out shock and surges that may be experienced when a motor is started-up. It works by temporarily reducing the load and torque in the power train during the start-up phase. It then gradually increases
the current and voltage supply from zero to full power. This has the effect of containing the electrical surge caused as the motor’s powerful internal electromagnets are energised. The effect of this is to reduce the
Stuart Harvey, MD of SoftstartUK
mechanical stress on the motor and shaft, as well as the electrodynamic stresses on the attached power cables and electrical distribution network. It not only ensures smooth, shock-free motor starting, but it also helps reduce breakdowns and maintenance requirements, which can be a major consideration on remote pumps. Ultimately it extends the life of the system. Harvey continued, “Devices are
Below: building the electrical panel for the multi-voltage pump test station
configured to control all three phases of the supply, although in some cases it is adequate to control just two phases. “Larger medium voltage soft starts use silicon controlled rectifiers (SCRs) in a series/parallel connection to share the heavy currents, and are preferred for applications like pumps, compressors and fans etc, when full torque is not necessarily required at start-up.”
INNOVATIVE USAGE However, the pump test station uses the soft start in a different and novel way. The voltage measurement transformers are configured in such a way that they provide very accurate metering of the voltage, as does the current transformer. They thus provide usable test data, voltage readings and power profiles during the start-up phase of each pump’s drive motor. From this data a comprehensive starting profile can be mapped out and used to develop a fully documented technical manual for each pump and its motor. “This documentation is very important, as it enables the pumps to be set-up and optimised. It is the main point of reference throughout the pumps’ working life (which on a capital pump is likely to be several decades),” concluded Harvey. Building the test station took five
months and was treated as a priority by SoftStart UK’s engineering team, to meet the delivery date.
Softstart UK
www.softstartuk.com T: 01493 660 510
/AUTOMATION
Enter 228 PLCS & INDUSTRIAL PCS | NOVEMBER 2014 S15
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