Excitation Board C98043-A7014-L1 6RY1703-0CA03 C98043A7014L1 6RY17030CA03 C98O43-A7O14-L1 6RY17O3-OCAO3

Siemens 6RY1703-0CA03 | SIMOREG DC Master 6RA70 Field Supply Board — Power Unit Field up to 600A, C98043-A7014-L1

Part Number: 6RY1703-0CA03

Manufacturer: Siemens AG (Germany)

Product Description: Power unit field up to 600 A

Board Reference: C98043-A7014-L1

Product Family: SIMOREG DC Master — 6RA70 Series Spare Parts (6RY17xx)

Product Lifecycle: PM300 — Active Product

Application: SIMOREG DC Master 6RA70 variable-speed DC motor drives

Function: Field supply power board — provides controlled DC current to the DC motor's field winding

Export Classification: AL: N / ECCN: N

Overview

The 6RY1703-0CA03 (board reference C98043-A7014-L1) is the field supply power board — the power unit for the motor field circuit — in the Siemens SIMOREG DC Master 6RA70 drive platform.

It is listed as an active product under Siemens' PM300 lifecycle classification, meaning it is currently manufactured and available through Siemens' spare parts supply chain. 

In DC motor drives, the field supply is a critical and distinct power circuit from the armature supply: the armature circuit delivers the high current that creates the motor's torque and rotational power, while the field circuit supplies the magnetising current that establishes the magnetic field in the motor's stator. Without the field, the motor produces no torque, regardless of the armature current.

The SIMOREG DC Master 6RA70 is Siemens' fourth-generation fully digital DC drive platform, covering armature currents from 15A to 1680A in the base drive configuration, with modular designs extending to much higher currents for large-scale industrial applications.

DC drives of this family are found in demanding industrial environments where the unique advantages of DC motor technology remain relevant: rolling mills, paper and board machines, extruder lines, mine hoists, printing presses, and test stands where precise torque control over a wide speed range is required.

The 6RY1703-0CA03 provides the controlled single-phase thyristor-based DC power for the motor field winding.

A strong, stable, and precisely regulated field current is fundamental to the DC drive's performance.

Field weakening — reducing the field current to extend the motor's speed range above base speed — is implemented by reducing the current delivered by this board. 

The regulation of field current directly determines the accuracy of the drive's field weakening control and the motor's ability to operate stably at extended speed.

Key Specifications

DC Motor Field Supply — Why It Matters

A DC motor's performance depends fundamentally on the quality of its field excitation. The field winding creates a magnetic flux in the air gap between the stator and rotor. The motor's torque output equals the product of this flux and the armature current. If the field current varies or becomes unstable, the motor's torque-producing capacity fluctuates — even if the armature current is perfectly regulated.

This is why the field supply circuit is a separate and carefully regulated sub-system within the 6RA70 drive.

The 6RY1703-0CA03 implements a controlled single-phase thyristor rectifier for the field supply. By adjusting the firing angle of the thyristors in response to the field current feedback signal, the board regulates the DC field current to the setpoint commanded by the drive's main microprocessor.

The regulation is closed-loop: field current is measured by a current transformer or Hall sensor, compared with the command value, and the firing angle is adjusted accordingly on each half-cycle of the supply.

This precise field current regulation enables two critical 6RA70 functions: field hold (maintaining rated field current during motor standstill or low-speed operation to ensure rapid torque response on acceleration) and field weakening (progressively reducing field current as the motor accelerates above base speed to extend the constant-power speed range). Both depend on the 6RY1703-0CA03 delivering accurate, stable field current under varying load conditions.

SIMOREG 6RA70 Drive Architecture

The 6RA70 drive is a modular system with a clear internal organisation. The power section handles the high-current armature supply — thyristor bridges convert three-phase AC from the supply into controlled DC for the motor armature.

The field supply section (where the 6RY1703-0CA03 operates) handles the motor field circuit separately.

The control electronics section (the CUD1 microprocessor board and optional option boards) runs the digital closed-loop control algorithms for both armature and field current.

The spare parts numbering for the 6RA70 uses the 6RY17xx prefix.

The 6RY1703 sub-family covers power unit boards — the boards that directly interface with and supply the motor circuits. Within this family, the field supply boards are identified by their board reference (C98043-A7014-L1 for the 6RY1703-0CA03) and their field current rating.

The companion board for larger drive configurations, covering higher field current applications, carries a different part number (6RY1703-0CA01 covering 140 to 510A).

Field Weakening — Extended Speed Control

Above base speed, the DC motor cannot increase its armature voltage further (the drive is at maximum output). To extend the speed range, the field current is reduced — field weakening.

As field current decreases, the magnetic flux decreases, and the motor's back-EMF drops for a given speed, allowing it to accelerate further at constant armature voltage. 

The torque capability decreases proportionally with flux, but in constant-power applications (winder drives, rolling mills, machine tool spindles), this is acceptable because the required torque also decreases at higher speed.

The 6RY1703-0CA03 must follow the field weakening command accurately and without delay.

A slow field weakening response limits the drive's dynamic performance.

A field supply fault during field weakening — causing sudden field loss — can cause a rapid uncontrolled acceleration (field failure runaway), a safety-critical event that the 6RA70's protection circuits are designed to detect and respond to.

The reliability of the field supply board is therefore not only a performance concern but a safety consideration in applications where field failure runaway could cause equipment damage or personnel risk.

FAQ

Q1: The 6RA70 drive generates a field current fault alarm (typically F060 or F061 in the SIMOREG alarm list). The motor field resistance has been measured and is correct. Is the 6RY1703-0CA03 the fault?

Field current fault alarms with confirmed-good motor field winding resistance suggest the field supply circuit is not delivering the commanded field current.

Before concluding the 6RY1703-0CA03 is faulty, check the single-phase AC supply to the field supply circuit — the field supply input voltage. 

If field supply voltage is present and within specification but the field current does not reach setpoint, the 6RY1703-0CA03's thyristors or firing circuit has failed and the board requires replacement.

Q2: The motor operates normally at low speeds but trips on overspeed at higher speeds. The armature voltage regulation appears correct. Could the 6RY1703-0CA03 be involved?

An overspeed trip at high speed with correct armature voltage regulation strongly suggests a field weakening problem — the field current is not reducing correctly as the speed increases. The 6RY1703-0CA03 controls the field current.

If the board is not responding correctly to field weakening commands (i.e., it is not reducing field current as commanded), the motor's back-EMF rises uncontrolled as speed increases. 

Verify the field current actual value on the drive's diagnostic display at the point where the trip occurs — if field current is not tracking the field weakening characteristic correctly, the field supply board or its feedback measurement is faulty.

Q3: The 6RY1703-0CA03 is described as having thyristors. When the board fails, can the thyristors be replaced separately, or does the entire board need replacement?

In principle, thyristor replacement on the board is a component-level repair that specialist service providers can undertake.

However, thyristor failure in a field supply circuit is often accompanied by damage to surrounding components — the gate drive circuitry, the current sensing circuit, and the snubber components may all have been stressed by the thyristor failure event. 

A complete board replacement is the more reliable approach for production-critical drives, as it restores the entire assembly to a known-good state rather than relying on a partially repaired board.

Q4: The 6RA70 drive has been out of service for an extended period. When recommissioning, should the field supply circuit be verified before running the motor?

Yes. After extended storage or shutdown, verify the single-phase AC supply to the 6RY1703-0CA03, check the field circuit connections at the motor terminals, and confirm the field current feedback signal is reaching the drive's control electronics.

Before commanding armature current, bring up the field supply alone and verify that field current reaches its rated setpoint and is stable.

Only after confirming stable field current should armature current be applied. Running with an unstable or absent field current risks loss of motor control.

Q5: The 6RY1703-0CA03 has PM300 Active lifecycle status. What does this mean for long-term availability?

PM300 Active means Siemens is currently manufacturing and supplying this product as a standard catalogue spare part. It is not scheduled for discontinuation in the near term.

For lifecycle planning purposes, PM300 Active is the optimal status for a spare part — it is the most secure availability position. 

Siemens provides advance notice (typically at least 3 years) before transitioning a product to PM500 (no longer available to order) status.

Purchasing ahead during PM300 Active status is the most cost-effective approach for critical spare stocking.