Output Filters Protect Motors

Jul 13, 2005 1:59 PM

From Transcoil comes the latest addition to the KLC-Series of motor protecting output filters. The V1000 (or V1K) features a smaller mechanical layout, but provides a high level of performance. The V1k limits peak voltage, increases voltage rise time and reduces common mode current by at least 30%.

Peak voltages in a 460-V system can reach 1200 V to 1600 V, causing rapid breakdown of motor insulation, leading to motor failure. On 575-V systems, the peak voltages can easily reach 2100 V. If this is left uncontrolled, insulation failure may occur. The same peak voltages that damage the motor can also damage the cable. Because the V1000 filters are designed to be placed at the output of the drive, these units also will protect the cable runs.

The added inductance of a V1000 filter also will help reduce motor heating, motor noise and motor vibration by reducing the current harmonics in the system.

Filtering also increases motor life. The V1000 reduces common-mode current by at least 30%. The V1000 substantially slows down the rate of change of the PWM switching as seen by the load. The slowing of the rate of change of the PWM switching increases the capacitive coupling impedance between bearings and bearing races. The increase in capacitive coupling, in turn, reduces the damaging common-mode currents and increases motor up-time. The V1000 reduces bearing, pitting and fluting.

The V1000 is guaranteed to limit motor terminal voltage to 150% of bus voltage (peak input voltage) when applied to the output of a VFD and ahead of a motor connected with up to 2000-ft leads, depending on carrier frequency and lead type and following the manufacturer’s guidelines. The V1K must be sized at no more than 110% of the drive output current rating.

Additional restrictions apply for multiple motor applications, so consult the factory. The V1K must be sized to have regular line current loading of no less than 25% of its current rating. If the load has a potential for overhauling, the drive must be equipped with braking resistors or other features limiting bus voltage to no more than the level of the peak line voltage. The V1K must be wired no more than 12 ft from the drive.

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