Application: Aerospace Wind Tunnel Research Center Refit

Replacement Part: New DC Drive Panel and Transformer

Wind tunnel DC drive

An aerospace research orientated wind tunnel centre needed to upgrade from an old MG Set on the main wind tunnel fan. The main wind tunnel fan was driven by a 1200HP 2300Amp DC motor which was working in tandem and used as a master speed reference for the main 11Kv 20,000Hp AC motor. The wind tunnel main DC motor base speed is 240 RPM, with an extended speed range using field weakening to a top speed of 500RPM. This provides an approximate top wind speed of Mach 1.2 (920mph)

Original Functional setup

The AC prime mover (motor) rotated the (generator) MG set at a fixed speed. The old system then modulated the field excitation to vary the DC output from the generator to the wind tunnel 1200HP DC motor. As the speed demand in the wind tunnel increased the load on the DC motor increased, this load (Armature Amps) was monitored by the system and either incremented or decremented the main plates in the salt bath to alter the power delivered to the 20,000HP AC motor. The starting system for the MG set was increasingly hazardous and troublesome as the prime mover was 11Kv and needed manual engagement via some old switch gear, this needed to be replaced.

New DC drive panel and Transformer

To provide good form factor and a reliable source of DC current to the wind tunnel 1200HP DC motor, a 12-pulse thyristor DC drive system was designed and built. The DC drive control panel was built to EN60204/1. This supplies the main DC motor directly, removing the need for the MG set. The panel main power is supplied from a new 11kV to 600VAC phase shift transformer installed locally to the main panel.  The speed demand was from an old motorised rheostat set up, operated from the main control desk. This old system was removed and the digital ramp used inside the new Parker SSD 590 series DC drive as the master speed reference for the wind tunnel. The DC loop from the old MG set was used and connected to the new inter-bridge reactor. Additional interlocks were interfaced to the DC drive panel which included interpole thermistors, field thermistors, air flow pressure switches, air temperature monitoring, and bearing temperatures.

The Parker SSD 590 DC drives are 4 quadrant (regenerative) and have the ability for rapid speed change. The drives are rated to the motor specification of 520VDC and 25% overload for 2hrs at 2300Amps armature current. The software inside the master monitored the total DC Armature current and calculated the I²T for the 2hrs overload rating.

During the commissioning, prior performance, dynamic response, and way points were recorded to provide speed reference points and guarantee the new system exceeded the dynamic performance of the old system.