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Carelabs

IEEE 1584 · Engineering

Motor Start Analysis Services in Portugal | Carelabs Experts

Motor Start Analysis. A motor starting study calculates the voltage dip and acceleration time a large motor causes at startup, confirming your system can bring it up to speed without nuisance tripping or instability elsewhere in the facility. Carelabs models across-the-line, autotransformer, reactor, and variable frequency drive starting methods and recommends the right one for your load.

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What starting does to the machine

A start is a mechanical event as much as an electrical one. Torque arrives suddenly, and couplings, belts, gearboxes and the driven process all absorb it.

What We Deliver

Torque through the acceleration

Motor torque is compared against the driven machine's speed-torque curve throughout the start, which identifies both insufficient margin, where the motor struggles, and excessive margin, where the drivetrain absorbs a shock it was not designed for.

WHY IT MATTERS

The electrical fix that breaks the machine

Starting problems are usually solved electrically and assessed electrically. A method chosen purely to reduce current draw can leave a drivetrain taking repeated shock loading, or a pump system absorbing transients it was never designed for.

  • Load speed-torque and inertia characteristics taken from the driven machine rather than assumed, since fans, pumps, compressors and conveyors behave very differently during acceleration.
  • Pressure transients considered on pump installations, because rapid acceleration and deceleration stress pipework, valves and joints.
  • Repeated starting duty assessed where the process demands it, as thermal limits rather than electrical ones usually govern permissible restart frequency.
  • Transformer impedance taken from test certificates where available, since typical values shift dip predictions materially on a weaker supply.
  • Protection verified against the real starting current so the motor is protected without tripping on a legitimate start.
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DELIVERABLES

What you receive

Issued against RTIEBT with the load characteristic, supply basis and modelling assumptions stated explicitly.

  1. 1Voltage dip profile at every bus through the acceleration period
  2. 2Torque and speed curves showing margin against the driven load throughout the start
  3. 3Assessment of mechanical stress on the drivetrain for each starting method considered
  4. 4Recommended starting arrangement with both electrical and mechanical reasoning stated
  5. 5Protection settings that accommodate the start while still protecting the motor
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How the study runs

01

Characterise the driven machine

We establish what is being started: its inertia, its breakaway torque and how it behaves through acceleration, since the load governs the outcome as much as the motor.

02

Establish the supply

Source impedance is derived from the distribution operator's fault level and transformer data, because dip depth follows supply strength directly.

03

Model the start

The motor is represented dynamically in ETAP and acceleration is simulated with voltage, current, torque and speed tracked throughout.

04

Assess both consequences

The electrical dip and the mechanical torque profile are evaluated together, so a method is not selected on one criterion while creating a problem on the other.

05

Compare the alternatives

Starting methods are tested on the same model, so the recommendation is made from simulation rather than from general preference or habit.

06

Report and settings

Findings are issued with the recommended arrangement and the protection settings that permit that start without compromising motor protection.

Frequently asked questions

Direct-on-line applies peak torque almost immediately, which on belt drives, couplings and gearboxes produces shock loading that accelerates wear. On pump systems it creates pressure transients that stress pipework and valves. Where a drivetrain fails repeatedly and nobody can explain why, the starting arrangement is worth examining.
Often, but not always. It reduces both starting current and the rate at which torque is applied, which helps electrically and mechanically. The limitation is that it also reduces available torque, so on a high-inertia or high-breakaway load it can produce a start that is too slow or does not complete. That case usually needs a variable speed drive.
It is set by the most sensitive load on the affected busbar rather than by a universal figure. Contactors typically release below roughly 70 to 80 percent of rated voltage and electronic equipment varies widely. This is why dip is reported at every bus rather than only at the motor being started.
Usually not, provided the supply and the driven load are unchanged. It becomes worthwhile where the installation has been extended since the original motor was commissioned, where the replacement is a different efficiency class with different starting behaviour, or where the driven machine has itself been modified.

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