Neometrix / Rail Test Equipment / Traction Motor Test Bench / NMX-TMB-72

NMX-TMB-72 · ENGINEERED-TO-ORDER CLASS — SPECIFY · SUPPLY · LOAD · BUILD · TEST · PROVE

Traction Motor Test Bench. A series motor must not run free.

Name: Traction Motor Test Bench
Brand: Neometrix
SKU: NMX-TMB-72

A traction motor comes back from overhaul with new insulation, a turned commutator and fresh bearings. None of it has been tried under power. The bench runs the motor, measures it, and keeps the record before it goes back under a locomotive.

For a DC series motor the run itself carries a risk: with no load, the speed climbs. So the bench has to supply the motor, load it or limit its speed, and compare every reading with the last.

Discuss a traction motor bench Capability note (PDF)

A single traction motor test bench on a plain white studio background, seen from the side: a long flat grey steel bed plate with machined slots carrying, in one straight line on a common shaft axis, a large cylindrical dark grey electric traction motor with a square terminal box on two cradle blocks, a bright torque-measuring shaft with a flexible coupling at each end under a perforated sheet steel guard, and a plain bright cylindrical load machine on two cradle blocks, and no people

Fig · 01 — A traction motor test bench: the motor under test, a torque-measuring shaft and a load machine on one bed and one axis, with a guard over the shaft — illustrative render.

The supply

variable and protecteda supply the bench can cut at once

The load

a load, or a speed limitnever a free-running series motor

The insulation

proved before powerresistance and high-voltage test first

The record

compared with the lastincoming readings against the final run

Status

engineered to orderno traction motor bench claimed

ISO 9001ISO 14001IEC 60349 reference standard

Overview

Why the whole job is the first run.

Because windings, commutator and bearings show their faults only when the motor turns under power, and the bench has to make that first run safe.

A single electric traction motor on a plain white studio background: a heavy cylindrical dark grey painted steel frame with a machined flange and a short splined output shaft at the front, a square terminal box on top, a round cooling air duct stub at the side, two lifting eyes and a pair of suspension lugs, and no people

Fig · 02 — A DC traction motor: a heavy round frame with a terminal box, a cooling air duct stub, lifting eyes and suspension lugs — illustrative render.

A series motor must not run free.

What the bench is for

It runs overhauled traction motors under power before they go back on a locomotive. It supplies the motor, gives it a load or a speed limit, measures what it draws and how it turns, and compares the result with the readings taken on the way in. It suits a DC traction motor and a converter-fed AC traction motor.

Why a series motor must not run free

In a series motor the field is carried by the armature current. As the load falls, the current falls, the field weakens and the speed rises. With no load at all, the speed can climb to a level that damages the motor.

A bench therefore never supplies a series motor and leaves it free. It loads the shaft or limits the speed first.

Why the insulation is proved before power

A motor that has just been rewound or cleaned can have damp or damaged insulation. The bench measures the insulation resistance and applies a high-voltage test before it applies power. Power applied to a damaged winding turns a small fault into a large one.

Why the motor is cleaned and dried first

Damp windings give false readings. The procedure therefore starts with a motor that is clean and dry.

Why every reading is compared with the last

The final run repeats the measurements taken when the motor came in and compares the two. A motor that is within limits can still be worse than it was, and the comparison shows it.

Why the bench has its own protection

An over-speed trip that cuts the supply has to work whatever the control system is doing. It is a separate device, and it is proved before any motor is run.

The method

Specify, supply, load, build, test, and prove.

Six steps in a fixed order. Choosing how the motor is loaded before anything is wired, and proving the over-speed trip before any motor is run, are the two a quick order skips.

1 · Specify

The motors to be tested, their types and their supplies are stated by the customer.

2 · Supply

A variable supply is chosen for each type of motor, direct current or a converter, with current limits and a way to cut it at once.

3 · Load

The way each motor is loaded, or its speed limited, is chosen before anything is wired.

4 · Build

The bed, the cradles, the couplings, the guards, the supply and the console are built as one installation.

5 · Test

The bench is proved on a known motor, and the over-speed trip is proved, before any customer motor is run.

6 · Prove

A record is kept for every motor, with its insulation readings, its run readings and the comparison with its incoming readings, and handed over with the bench.

How to load the motor under test

Method	How it works	What to watch
A light load with an over-speed trip	the motor runs on a variable supply with a small load on the shaft, and a trip cuts the supply at a set speed	it is simple and quick for the routine run after overhaul, but it proves little about the motor under load, and the trip has to be proved first
A load machine on the shaft	a second machine, driven or braking, holds a stated load on the motor through a torque-measuring coupling	it proves the motor under load and measures the torque, but it needs a second machine and a controlled supply for it
A back-to-back pair	two motors are coupled, one driving and one generating, so that the supply has to cover only the losses	it suits long runs and saves power, but it needs two matched machines, and equal loading is hard to hold

The step people underrate is proving the over-speed trip. A bench whose trip has never been tried has only a hope that the motor will stop.

Work content

What the bench contains, element by element.

Read it as a checklist: a bench missing a row will pass a motor on paper and not under the locomotive.

A single wound traction motor armature on a plain white studio background: a bright steel shaft carrying a laminated steel core with copper winding ends and a copper commutator of many fine segments, with a bearing seat at each end, and no people

Fig · 03 — A traction motor armature: a laminated core, winding ends and a copper commutator on a steel shaft — illustrative render.

Element	What it does	What matters
Bench bed and cradles	carry the motor and its load	heavy and flat, with machined slots, so that the motor, the coupling and the load stay in line
Variable supply	powers the motor	a supply for DC motors and a converter for AC motors, with current limits and a way to cut it at once
Load machine or brake	loads the shaft	holds a stated load on the motor, or takes the power from it, so that a series motor never runs free
Torque-measuring coupling	joins motor to load	carries the turning, measures the torque and takes no side load from a slight misalignment
Over-speed protection	cuts the supply	a separate trip at a set speed that acts whatever the control system is doing
Measurement	reads the motor	voltage, current, speed, torque, temperature and vibration, logged against time
Insulation test set	proves the windings	insulation resistance and a high-voltage test before power, and again after the run
Guards and interlocks	protect people	a guard over every rotating shaft, and a door interlock that cuts the supply when the door is opened
Test console and record	run the test plan	the steps, the readings and the comparison with the motor's incoming readings, kept for every motor
Procedure	fixes the sequence	specify, supply, load, build, test and prove, the same for every motor
Testing & documentation	prove the bench first	the trip and the load proved on a known motor before any customer motor, and a record the customer can inspect

The elements that decide whether the bench is safe are the load and the over-speed trip, because a series motor that loses its load can reach a speed that damages it within moments.

Full specification — expand

System	A heavy bench bed with machined slots and cradles that carry the motor and its load on one axis; a variable supply for DC motors and a converter for AC motors, with current limits and a way to cut the supply at once; a load machine or a brake; a torque-measuring coupling; a separate over-speed trip; measurement of voltage, current, speed, torque, temperature and vibration; an insulation test set; guards and door interlocks; a test console with the test plan and a record for every motor, including the comparison with its incoming readings; a written test plan; and testing and documentation before handover
The One Idea	A series motor must not run free.
Why A Series Motor Must Not Run Free	In a series motor the field is carried by the armature current, so as the load falls the current falls, the field weakens and the speed rises, and with no load at all the speed can climb to a level that damages the motor, which is why a bench loads the shaft or limits the speed before it gives the motor power
Why The Insulation Is Proved Before Power	A motor that has just been rewound or cleaned can have damp or damaged insulation, so the bench measures the insulation resistance and applies a high-voltage test before it applies power, because power applied to a damaged winding turns a small fault into a large one
Why The Motor Is Cleaned And Dried First	Damp windings give false readings, so the procedure starts with a motor that is clean and dry
Why Every Reading Is Compared With The Last	The final run repeats the measurements taken when the motor came in and compares the two, because a motor that is within limits can still be worse than it was, and the comparison shows it
Why The Bench Has Its Own Protection	An over-speed trip that cuts the supply has to work whatever the control system is doing, so it is a separate device and it is proved before any motor is run
Standards	IEC 60349-1 covers rotating machines for rail traction other than converter-fed AC motors, including DC traction motors, and IEC 60349-2 covers converter-fed AC motors. This page prints none of their limits, test levels, speeds, currents or times, and no edition year: those come from the standard the customer names and from the motor. Approval of a bench or of a motor rests with the customer and the authority they name; none is claimed here
Configurations	A DC motor bench with a supply, a load and a trip, an AC motor bench with a converter and a no-load run, and a back-to-back bench for long runs
Scope Boundary	This page is the traction motor test bench. It is not an e-motor test bench, which develops and maps electric motors on a four-quadrant dynamometer (see e-motor test bench), not a speedometer test bench (see speedometer test bench) and not a bogie rig (see rail bogie test rig and turntable). A winding line, a commutator lathe and a balancing machine are different equipment again. No certification is claimed here
Status	Neometrix engineers traction motor test benches to order, and no delivered traction motor test bench is claimed.

Configurations

One method, three ways to build the bench.

The method, the insulation test and the record are shared. What changes is the supply and how the motor is loaded.

DC motor bench

Supply, load and trip

A variable DC supply, a load machine and an over-speed trip, for series-wound traction motors that must never run free.

AC motor bench

Converter and no-load run

A converter that supplies the voltage and the frequency, for the no-load run and the checks of converter-fed AC traction motors.

Back-to-back bench

Two motors, one supply for the losses

Two coupled motors, one driving and one generating, for long runs where the supply has to cover only the losses.

And the part that is not equipment at all, yet decides all three: the test plan. It fixes the order of the tests, how the motor is loaded, when the trip is proved, and what is recorded and compared. It is written from the motors, not from the supply.

Where it is used

Wherever a motor is trusted again, and has to prove it first.

The common thread is a motor that has been opened, repaired and closed again, and has to run under a locomotive without a second visit.

Locomotive sheds

Where traction motors come off a locomotive for overhaul and must be proved before they go back.

Traction motor overhaul shops

Where motors are stripped, rewound, turned and rebuilt, and each one needs the same run and the same record.

Winding and repair shops

Where a rewound motor has to show that its insulation and its run are as good as when it came in, or better.

Acceptance of repaired motors

Where a motor returns from an outside repairer and the owner wants an independent run before it is fitted.

Watch

See it in motion.

A short walkthrough video of the traction motor test bench.

FAQ

Common questions.

Longer answers, for readers who want the reasoning.

Q · 01 What does a traction motor test bench actually do?

It runs an overhauled traction motor under power before the motor goes back on a locomotive. It measures the insulation and tries it at high voltage, supplies the motor, gives it a load or a speed limit, and reads voltage, current, speed, torque, temperature and vibration. It then compares the readings with those taken when the motor came in and keeps the record. It does not overhaul the motor, it does not wind it, and it does not replace a trial on the locomotive.

Q · 02 Why must a series motor not run free?

Because in a series motor the field is carried by the armature current. When the load falls, the current falls, the field weakens and the speed rises. That raises the speed further, and with no load at all it can climb to a level at which the rotor is damaged by the forces on it. A traction motor is built to work against a load, so a bench never leaves it free. It either loads the shaft or limits the speed, and a separate trip stands behind both. An AC motor fed by a converter does not behave this way, which is why its no-load run is a routine test.

Q · 03 Why is the insulation proved before the motor is powered?

Because a motor that has been rewound, cleaned or stored can have damp or damaged insulation, and power applied to it can turn a small fault into a large one. The bench measures the insulation resistance first and applies a high-voltage test before power, and it repeats both after the run. The motor is also cleaned and dried before any of this, because damp windings give false readings and a good motor can look bad, or a bad one good.

Q · 04 Why is every reading compared with the last?

Because passing a limit is not the same as being as good as before. The bench repeats the measurements taken when the motor came in and compares the two sets. A motor that is within limits can still be worse than it was, with more current for the same speed or more vibration, and the comparison shows it. The record also lets a shed see a trend across many motors, which a single pass or fail never shows.

Q · 05 Is this the same as the e-motor bench, the speedometer bench or the bogie rig?

No, and the differences are worth stating precisely. The e-motor test bench page covers developing and mapping electric motors on a four-quadrant dynamometer. The speedometer test bench page covers checking a speed indicator against a reference. The rail bogie test rig and turntable page covers the equipment that proves a bogie. This page is the traction motor test bench. A winding line, a commutator lathe and a balancing machine are different equipment again. It does not replace any of them, and it does not claim what they claim a second time.

Q · 06 Has Neometrix built one of these?

We would rather answer this plainly than let a page imply otherwise. Neometrix engineers traction motor test benches to order, and no delivered traction motor test bench is claimed. What stands behind the offer is adjacent: Neometrix engineers an e-motor test bench (see the e-motor test bench page), a speedometer test bench (see the speedometer test bench page) and a rail bogie test rig (see the rail bogie test rig and turntable page). The supplies, converters, load machines, torque transducers and insulation test sets are catalogue items, bought in, not invented. What Neometrix engineers is the bench around them: the bed and cradles, the couplings and guards, the protection, the console and the record, the procedure and the test plan. So the honest position is that the bench is engineered to order, the neighbouring disciplines are in the building, and the first bench of this exact kind will be built around the customer's own motors rather than taken off a shelf.

Q · 07 Which standard applies, and what can the bench not do?

IEC 60349-1 covers rotating machines for rail traction other than converter-fed AC motors, including DC traction motors, and IEC 60349-2 covers converter-fed AC motors. This page prints none of their limits, test levels, speeds, currents or times, and no edition year: those come from the standard the customer names and from the motor. The bench tests a motor and keeps a record. It does not certify a motor or a locomotive: this page claims no certification or accreditation. No speed, voltage, current, time or quantity figure is printed here, and approval for use rests with the customer and the authority they name; none is claimed here.

Q · 08 What do you need from us to quote?

Six things, and most of them describe your motors rather than the bench. First, the motors: the types to be tested, DC or AC, and how many types there are. Second, the supply: what each type needs and what the shed can provide. Third, the load: whether you want a light load, a load machine or a back-to-back pair. Fourth, the tests: the insulation tests and the readings you want taken. Fifth, the throughput: how many motors are run in a week. Sixth, the record: what you want kept and compared for each motor. From that we come back with a bench concept, a written test plan you can check, and a budgetary price.

The neighbouring rail and motor pages, and how they differ from this one.

Three neighbours: one checks an instrument, one develops a motor, one proves a bogie.

↗ An instrument

Speedometer Test Bench

Benches that check a speed indicator against a reference - an instrument bench, where this page runs a motor.

↗ Developing a motor

E-Motor Test Bench

Four-quadrant dynamometer benches for developing and mapping electric motors - development and mapping, where this page runs an overhauled motor and keeps the record.

↗ The bogie

Rail Bogie Test Rig & Turntable

Rigs that prove a bogie before it goes back under a coach - a structure, where this page proves a motor before it goes back under a locomotive.

Browse all Neometrix product lines.

Get a quotation

Tell us the motors, the supply,
and how you want them loaded.

The projects desk replies within two working days with a bench concept, a written test plan you can check, and a budgetary quotation. Write to [email protected] or use the form.

Enquire — traction motor bench Capability sheet (PDF) +91 7777 876 876

ISO 9001 / 14001 ENGINEERED-TO-ORDER CLASS — TRACTION MOTOR TEST BENCH SPECIFY · SUPPLY · LOAD · BUILD · TEST · PROVE — A SERIES MOTOR MUST NOT RUN FREE ENGINEERED IN NOIDA · INDIA