Monday, 6 January 2020


Guest Post by James L. Gordon

What else can go wrong – this one is a doozy!

There are 3 synchronous condensers (SD) at the Soldiers Pond substation on the Avalon         
Peninsula, the down-power end of the DC transmission line.

Muskrat synchronous condenser.
In electrical engineering, a synchronous condenser (sometimes called a synchronous capacitor or synchronous compensator) is a DC-excited synchronous motor, whose shaft is not connected to anything but spins freely. Its purpose is not to convert electric power to mechanical power or vice versa, but to adjust conditions on the electric power transmission grid. Its field is controlled by a voltage regulator to either generate or absorb reactive power as needed to adjust the grid's voltage, or to improve power factor. The condenser’s installation and operation are identical to large electric motors and generators.
Muskrat synchronous condenser.
Increasing the device's field excitation results in its furnishing reactive power (measured in units of var) to the system. Its principal advantage is the ease with which the amount of correction can be adjusted. The kinetic energy stored in the rotor of the machine can help stabilize a power system during rapid fluctuations of loads such as those created by short circuits or electric arc furnaces. Large installations of synchronous condensers are sometimes used in association with high-voltage direct current converter stations to supply reactive power to the alternating current grid.
Source – Wikipedia.

Muskrat synchronous condenser flywheel (red)
The SD consists of a heavy rotor and flywheel suspended between two bearings. Once assembled, the rotor has to be turned through 180 degrees on a regular basis to avoid the shaft bending by a few thou (one thou is equal to one thousandth of an inch) due to the weight. The machinists assembling advised NALCOR to do this, but the advice was ignored. I checked this with an experienced machinist working on the Pickering nuclear plant in Ontario, and he said the advice was correct.
The result – one condenser vibrates on rotation, and in the other two, presumably finished earlier, the shaft deflection is so large that the rotor comes in contact with the stator.
There is no fix – a new shaft has to be ordered, the CD’s dismantled and re-assembled, which will take between 1 and 2 years! The transmission line cannot operate without the condensers.

Jim Gordon.