On the display
The panel prints VSD - HIGH TOTAL DEMAND DISTORTION. The manuals give this text in only one form, and they place it among the safety shutdown messages of the chiller, so the wording on the display announces a safety shutdown condition.
What it means
The shutdown indicates that the input current to the VSD is not sinusoidal. The quantity behind the message is TDD, or Total Demand Distortion. Both manuals define TDD through IEEE Std 519-1992, where the term stands for the total root-sum-square harmonic current distortion, expressed in percent of the maximum demand load current (a 15 or 30 min demand). The value shown on the display is the total RMS value of all the harmonic current supplied by the main power to the VSD, divided by the chiller Full Load Amps and given as a percent. The second manual phrases this same display value as the sum of the harmonic currents supplied by the main power to the VSD, divided by the Full Load Amps.
Why it appears
- The input current to the VSD is not sinusoidal.
- The shutdown occurs if the TDD exceeds 25% continuously for 45 seconds.
Setpoints and thresholds
- Shutdown condition: TDD above 25%, held continuously for 45 seconds.
- Definition basis: IEEE Std 519-1992 — total root-sum-square harmonic current distortion, in percent of the maximum demand load current (15 or 30 min demand).
- Display basis: total RMS value of all harmonic current supplied by the main power to the VSD, divided by the chiller Full Load Amps, in percent.
Reset and restart
Recovery from this shutdown is a single action: The chiller can be started after the CLEAR FAULT button is pressed.
Questions engineers ask
What does VSD - HIGH TOTAL DEMAND DISTORTION mean on a YORK YMC2?
It is a safety shutdown indicating that the input current to the VSD is not sinusoidal. The message appears when the TDD of that input current exceeds 25% continuously for 45 seconds.
What is TDD on the YMC2 and how is the displayed value calculated?
TDD (Total Demand Distortion) is defined by IEEE Std 519-1992 as the total root-sum-square harmonic current distortion in percent of the maximum demand load current (15 or 30 min demand). The display shows the total RMS value of all harmonic current supplied by the main power to the VSD, divided by the chiller Full Load Amps, as a percent.
How do I clear VSD - HIGH TOTAL DEMAND DISTORTION and restart the chiller?
The chiller can be started after the CLEAR FAULT button is pressed. That single action is the recovery the manuals describe for this shutdown.
Messages next to this one
Source
Written from the manufacturer's manuals for the YORK YMC2; every number and designation on this page is checked against them before publication. The row of the manual this message comes from:
All YORK YMC2 messages: fault codes · YORK YMC2 documentation · YORK manuals