Top Drive Commissioning with Siemens PLCs Field Service Reference

Overview

Top Drive systems are the rotating heart of modern drilling rigs, hoisting and rotating the drill string while supporting downhole mud circulation. On National Oilwell Varco (NOV) installations, the controls backbone is overwhelmingly Siemens-based: S7-300 / S7-400 PLCs for the main control cabinet, SINAMICS S120 drives for the main AC motor and brake management, ET200 distributed I/O over Profibus DP / Profinet at the remote panels, and WinCC flexible or WinCC (TIA Portal) on the driller's HMI. This reference consolidates the field-proven workflow used by Field Service Technicians (FSTs) when they are sent for on-the-job (OJT) commissioning of these systems at international shipyards and on land rigs.

The objective is to walk an FST or controls engineer through the same sequence NOV training typically exposes new technicians to: classroom architecture familiarization, derrick and drawworks I/O walk-down, mud pump room integration, PLC-online supervised programming, and acceptance testing before hand-off to the driller. The skills translate directly to drilling controls, FPSO conversion work, and downstream oil-and-gas automation.

System Architecture

The NOV Top Drive control system is built around a redundant, modular PLC backbone. The hardware hierarchy from the driller's console down to the motor is as follows:

Typical I/O counts on a TDS-500 / TDS-1000 class Top Drive:

• Digital Inputs: 192 (limit switches, contactors, pushbuttons, E-Stops)
• Digital Outputs: 128 (contactor coils, solenoid valves, indicators)
• Analog Inputs: 24 (4-20 mA pressure, load cell, position feedback)
• Analog Outputs: 8 (drive reference, valve commands)
• Profibus slaves: 6–12 (drive, I/O stations, third-party chillers, hydraulic power unit)

Prerequisites for Commissioning

Before stepping on the rig, an FST must have completed the in-house NOV controls training and be in possession of:

1. Valid BOSIET (Basic Offshore Safety Induction and Emergency Training) certificate, including HUET and sea-survival, mandatory for any platform work.
2. CompEx Ex01–Ex04 hazardous-area certification for work on or near Zone 1 electrical equipment (typical cost USD $2,800 in Singapore at the time of writing).
3. Siemens Step 7 V5.5 or TIA Portal V17+ with the Top Drive project archive (.s7p / .ap17) and the matching PLC password set issued by NOV Controls Division.
4. Sinamics STARTER V5.4 or Startdrive V17 for drive parameterization and trace capture.
5. A calibrated megger (1 kV), ground-bond tester, hydraulic pressure gauge set, and a Profibus diagnostic tool (e.g., Softing PROFINET-INspektor or Siemens BT200).
6. Rig-specific single-line drawings, the P&ID for the mud circulation loop, and the approved functional specification (FS) signed by NOV Controls Engineering.

I/O Simulation Procedure (Pre-Power Walk-Down)

The first rotation an FST performs after arriving on the rig is the I/O simulation pass. The Top Drive cabinet is still de-energized at the upstream breaker; 24 VDC control power is on. The goal is to verify, in the PLC online editor, that every field termination lands on the correct input/output word and that the diagnostic message strings match the P&ID tag names.

1. Connect to the PLC. Open TIA Portal → Project tree → "Online → Go online" using the rig's commissioning Ethernet cable. Confirm the device name (e.g., PLC-TDS500-01) and IP address (typical 192.168.0.10/24) match the as-built network plan.
2. Force a known digital input. From the driller's console, momentarily press the IBOP Close pushbutton. In the PLC tag table, monitor tag IBOP_CLOSED_DI in IW0. The bit must transition 0 → 1 → 0 within the debounce time (default 50 ms in the OB1 cyclic interrupt OB35).
3. Force each digital output in turn. Navigate to Watch & Force, force CONTACTOR_K1_DO in QW2 to TRUE and confirm the contactor closes. Listen for the contactor pull-in and verify the auxiliary contact echoes back through its corresponding DI within 200 ms. Never force an output without first verifying the field wiring is correct and the contactor is not feeding an energized motor circuit.
4. Verify analog scaling. Inject 4 mA and 20 mA into the load cell input using a calibrator. The PLC reading at HOOKLOAD_AI (PIW 288) should map to 0 lb and 1,000,000 lb respectively per the scale block in FB305. Confirm the engineering units and the alarm thresholds at 90 % and 110 % of full scale.
5. Profibus node check. From TIA Portal, Online & Diagnostics → PROFIBUS DP. Every slave must appear in green with no diagnostic interrupts. A missing node usually means a terminated drop is open or a slave address switch is set wrong — typical default node addresses are 3 (drive), 4–6 (ET200S), 8 (chiller), 9 (HPU).

Ladder Logic and State Machine Verification

The Top Drive control is implemented as a state machine in Function Block Diagram (FBD) inside FB200 TDS_MainSequence. The states and their transitions are:

To verify the state machine in the field, an FST adds the state variable to a VAT and forces transitions using the driller's panel while monitoring in online mode. Typical ladder snippet (LAD) for the MAKEUP entry guard:

|   MAKEUP_BTN_PB    DRILLING_ACTIVE   IBOP_OPEN_DI   MAKUP_PERMIT   |
|----| |--------------| /|-------------|/|--------------( )-----------( )----( S )  STATE_DB.DBX2.0

Supervised Programming Workflow

NOV does not permit FSTs to make unsupervised programming changes to production rig code. The approved workflow is:

1. Document the required change on a Field Change Request (FCR) form, signed by the Controls Engineer in Houston.
2. Download the project archive from the engineering server, make the change in a separate working copy, and produce a diff report.
3. Connect to the PLC online, perform the change in a single write operation with a peer (the Controls Engineer) watching the trace.
4. Verify the change with a controlled test (e.g., force the new input, observe the new output).
5. Save the archive with a version increment (e.g., TDS500_v04_07.S7P) and email it back to Controls Engineering before leaving the rig.

Field Commissioning Sequence (Top Drive to Mud Pump Room)

The full commissioning walk-down follows the physical path from the derrick down to the mud pump room, energizing one system at a time.

1. Derrick — Crown block and traveling block. Verify limit switches at top of stroke (LS_TOP) and bottom (LS_BOT), crown-o-matic proximity sensor, and the encoder on the deadline. Confirm BLOCK_HEIGHT_MM in the HMI matches a tape-measure reference within ±50 mm.
2. Top Drive — Main frame and counterweight. Inspect the IBOP (inner blowout preventer) open/close limit, link tilt switch, and counterweight hydraulic cylinder LVDT. Force the counterweight extend and retract solenoids and confirm FB312 reports OK.
3. SCR / VFD house. With the upstream breaker open, megger each motor feeder phase-to-phase and phase-to-ground at 1 kV (minimum 100 MΩ for a 600 V AC motor). Verify SINAMICS S120 parameter r0027 (actual current) reads 0 A with no command.
4. First motor rotation (unloaded). Command a slow-speed rotation of 5 RPM from the drive commissioning tool. Verify rotation direction matches the engraved arrow on the gearbox. If reversed, swap two phases at the motor junction box — never at the drive output, because that breaks parameter p1820 direction logic.
5. Brake verification. The holding brake is controlled by SINAMICS via the Brake Control Word (p1215). With the motor stopped, command a 1 % torque setpoint and check that the brake releases within 250 ms and re-engages on stop command within 150 ms.
6. Drawworks and mud pump integration. From the driller's console, run the drawwworks hoist at 0.5 m/s while a colleague monitors mud pump #1 stroke counter at the pump. Verify the interlock FB450 MUD_PRESS_LOW blocks hoisting if standpipe pressure drops below 1.7 MPa (250 psi).
7. HMI alarm test. Trip each of the 16 critical alarms in turn (over-torque, over-current, low hydraulic, high motor temp, IBOP fail, E-Stop, Profibus fault, encoder fault, hydraulic over-pressure, etc.) and confirm the correct alarm banner, color, and acknowledge behavior in WinCC.

VFD and Motor Control Parameters

The SINAMICS S120 must be parameterized to match the Top Drive motor nameplate before any rotation. Key parameters from the as-built commissioning sheet:

For three-phase apparent power sizing of the supply feeder, use the standard formula:

kVA = sqrt(3) × V_LL × I_line / 1000
     = 1.732 × 575 × 360 / 1000
     = 358.5 kVA

If the 360 A figure were instead a single-phase or per-phase value, the calculation would change accordingly. Always confirm on the motor nameplate whether the current is three-phase line, single-phase, peak, or RMS before sizing upstream feeders or transformers.

Common Fault Codes and Diagnostics

Top Drive faults surface in two places: as PLC-generated alarms in WinCC (DB500) and as SINAMICS drive faults (F-code). The matrix below maps the most common field events:

Working Hours, Rotation, and Field Health

Install-and-commission (I&C) rotation on a NOV Top Drive commissioning is typically 16 hours/day, 7 days/week for the duration of the rig acceptance. Land-rig FSTs usually work standard 8-hour shifts with a regular rotation, but the I&C phase always trends to long hours. Offshore 28/28 rotation (28 days on, 28 days off) is mandatory; you cannot work more than 28 continuous days offshore per most flag-state regulations and NOV internal policy.

Training Pathway and Competency Map

NOV does not require a four-year degree for FST entry. Roughly one third of each training cohort enters as ex-military, one third with an associate degree or technical certificate, and one third with no prior qualification. The technical competencies NOV expects a competent FST to demonstrate within 12 months are:

Career Path and Compensation Benchmarks

The typical NOV FST career ladder with realistic U.S. figures (subject to region and rig assignment):

Compensation is heavily weighted by rig bonus (sometimes equal to base pay), per diem for international rotations, and hazard pay for offshore work. A first-year trainee with no experience can realistically clear $90k if they take the long rotations, but the trade-off is consistent 16-hour days for months at a time.

Regional Hotspots and Hiring Patterns

Where the work is:

• Houston, TX (USA) — NOV headquarters; all Top Drive training originates here. Strongest concentration of controls engineering roles.
• Alberta, Canada — Fastest-growing North American land development. NOV, Precision Drilling, and Ensign all hire aggressively. Good entry point for Canadian expats returning home.
• North Dakota, USA (Bakken) — Land-rig activity; less controls work than Alberta but more mechanical.
• Singapore — Recognized as South-East Asia's oil & gas hub; reportedly ~70 % worldwide market share of FPSO conversions and jack-up rig construction. Major shipyards Keppel, Sembcorp, and Samsung Heavy Industries (Geoje Island, Korea) commission NOV Top Drives here.
• Geoje Island, Korea — Samsung Heavy Industries shipyard. Active commissioning of newbuild rigs and drill-ships.
• Brazil (pre-salt) — Major deepwater market; FSTs from NOV's International Group typically rotate here for First Well Support on rigs they helped commission.

Documentation and Version Control

NOV Controls Division maintains the project archive on a controlled server. After every field change, the FST must:

1. Save the project archive with version tag _v<major>_<minor>.
2. Update the FCR register with the change description.
3. Upload the archive to the engineering server via the rig's VSAT or shore connection.
4. Email the Controls Engineer and the rig superintendent with the diff.

Failure to follow this sequence is the most common reason commissioning trips to the next rig — the next FST inherits an undocumented state.

Verification Checklist Before Hand-Off

Before signing the acceptance test memo with the driller, run this final pass:

FAQ