Danfoss VLT AQUA Drive Design Manual

Also see for vlt aqua: Instructions Design guide Instruction manual Operating instructions Design guide

Contents

Lead Pump AlternationThe motors must be of equal size. This function makes it possible to cycle the drive between thepumps in the system (maximum of 2 pumps). In this operation, the run time between pumps isequalized, thus reducing the required pump maintenance and increasing reliability and systemlifetime. The alternation of the lead pump can take place at a command signal or at staging (addinganother pump).The command can be a manual alternation or an alternation event signal. If the alternation eventis selected, the lead pump alternation takes place every time the event occurs. Selections include:whenever an alternation timer expires, at a predefined time of day, or when the lead pump enterssleep mode. Staging is determined by the actual system load.A separate parameter limit's alternation is only to take place if the total capacity required is >50%. Total pump capacity is determined as the sum of the capacities of the lead pump and thefixed speed pumps.Bandwidth ManagementTo avoid frequent switching of fixed speed pumps in cascade control systems, the desired systempressure is kept within a bandwidth rather than at a constant level. Staging bandwidth providesthe required bandwidth for operation. When a large and quick change in system pressure occurs,the override bandwidth overrides the staging bandwidth to prevent immediate response to a shortduration pressure change. An override bandwidth timer can be programmed to prevent staginguntil the system pressure has stabilized and normal control has been established.When the cascade controller is enabled and the drive issues a trip alarm, the system head ismaintained by staging and de-staging fixed speed pumps. To prevent frequent staging and de-staging and minimize pressure fluctuations, a wider fixed speed bandwidth is used instead of thestaging bandwidth.6.1.9. Pump Staging with Lead Pump AlternationWith lead pump alternation enabled, a maxi-mum of two pumps are controlled. At an al-ternation command, the PID stops, the leadpump ramps to minimum frequency (fmin),and after a delay, ramps to maximum fre-quency (fmax). When the speed of the leadpump reaches the de-staging frequency, thefixed speed pump will be cut out (de-staged).The lead pump continues to ramp up, thenramps down to a stop, and the two relays arecut out.After a time delay, the relay for the fixed speed pump cuts in (staged), and this pump becomesthe new lead pump. The new lead pump ramps up to maximum speed and then down to minimumspeed. When ramping down and reaching the staging frequency, the old lead pump is now cut in(staged) on the lines as the new fixed speed pump.If the lead pump has been running at minimum frequency (fmin) for a programmed amount oftime with a fixed speed pump running, the lead pump contributes little to the system. When the6. Application Examples VLT® AQUA Drive Design Guide118 MG.20.N2.22 - VLT® is a registered Danfoss trademark.6