Delta MM300 Instruction Manual download pdf (Page 136)

CHAPTER 6: SETPOINTS CONTROL ELEMENTS

MM300 MOTOR MANAGEMENT SYSTEM – INSTRUCTION MANUAL 6–49

Test Manual Mode

Range: On, Off, Unaffected

Default: On

When the test switch is on, this setpoint determines if the manual mode is forced on,

forced off, or is unaffected.

6.4.1.2 Stop/start control element

An external stop sequence has occurred if the relay detects that either contactor A or

contactor B has dropped out without receiving a stop command. If the

External Stop Action

setpoint is programmed as “Stop”, the relay will accept this as a stop control and display

the

External Stop message. If this setpoint is set to “Trip”, the relay will treat this as an

emergency stop trip. This trip condition must be reset before the motor can be restarted.

Most protection and control elements in this relay are sensitive to whether the motor is

stopped, starting, or running. These include the jam, acceleration, undercurrent,

underpower, overvoltage, and undervoltage protection, the process interlocks, and the

thermal start inhibit and undervoltage restart elements.

Traditionally, the motor is deemed to have entered the starting state when the motor

current changes from zero to some measurable value, and to have entered the running

state when the current having increased above FLA then subsides below FLA. This

algorithm is satisfactory for most applications. The current profile of full voltage across-

the-line starters for instance typically goes from zero to 6 × FLA within a cycle of the

contactor closing, and then decays exponentially until it reaches 1 × FLA just before

reaching normal operating speed.

However, some starter types implemented in the MM300 have significantly different

current profiles. For instance, with an inverter starter, the inverter may ramp the motor

speed up so slowly that the current never exceeds FLA. Alternatively, the current may

initially exceed 1 × FLA, but subside well before reaching normal operating speed. The

traditional algorithm could either not declare the motor reaching the running state, or

declare it much too soon.

Another problem can develop when there is a brief supply interruption for which the

immediate undervoltage restart feature recloses the contactor so quickly that there is little

or no inrush current.

The traditional algorithm would detect the start (if it is fast enough), but may or may not

detect the running state that follows. Even if it does detect the running state, as it is an

atypical start, the learned values such as learned acceleration time would be corrupted.

The MM300 employs an improved starting and running state detection algorithm.

Normally, it declares starting when either contactor A or contactor B closes. Running is

declared when either contactor has been closed for one second, and then current is found

to be below 1 × FLA. This provides equivalent functionality to the traditional algorithm.

However, the advanced algorithm also accepts Starting Status Block and Running Status

Block signals. Most starter types leave these signals in their default off state, where they

have no effect on the starting and running declarations. Where required however, the

starters can manipulate these signals to correct the above described problems with the

traditional algorithm. The inverter starter for instance asserts the Starting Status Block

signal when it powers up the inverter, and then allows the starting state to be declared by

turning it off only when the ramp up command is issued. The inverter starter also asserts

the Running Status Block signal and then allows the running state to be declared by

turning it off only when the inverter signals up-to-speed.

In addition, the advanced algorithm accepts a UVR Short Dip signal from the

undervoltage restart element. This signal will carry the running status through short dips

followed by immediate reclose.

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Delta MM300 Instruction Manual Page 136

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