Solcon - IGEL

Soft Starter vs VFD

yosi.frank@solconigel.com (Yosi Frank) — Wed, 15 Apr 2026 10:52:07 GMT

Which Is Right for Your Application?

ears

Walk into any industrial electrical panel shop and you will find both soft starters and variable frequency drives (VFDs). They are often grouped under the same category of “motor starters,” and both reduce starting current.

However, selecting the correct solution is not interchangeable. The choice directly impacts capital cost, system stability, and long-term operational efficiency.

At its core, the decision comes down to one question:

Ι Does the motor need to operate at variable speed, or does it run at a fixed speed? Ι

The One-Sentence Rule

Use a soft starter for fixed-speed applications.
Use a VFD when variable speed is required.

In most cases, this rule holds. The complexity lies in how the application behaves in real operating conditions.

Scenario 1: Municipal Water Supply Pump

A 250 kW centrifugal pump operates at a constant speed, with flow controlled downstream. It starts several times per day.
• Fixed-speed operation
• High inrush current without control
• Risk of water hammer during stopping

A soft starter enables controlled acceleration and deceleration, reducing both electrical and hydraulic stress.

Conclusion: Soft starter is the correct and cost-effective solution.

....................................................................................

Scenario 2: HVAC Air Handling Unit (Variable Demand)

A 90 kW fan adjusts output based on occupancy and environmental conditions.
• Variable speed required
• Energy consumption follows the cube law
• Significant operating hours

A VFD enables speed control and delivers substantial energy savings over time.

Conclusion: VFD is required both functionally and economically.

....................................................................................

Scenario 3: Mining Conveyor (Loaded Start)

A 400 kW conveyor starts under load with high inertia.
• Fixed operating speed
• High starting torque requirement
• Controlled acceleration is critical

A soft starter can manage acceleration effectively in most cases. A VFD is only justified where precise torque profiling is essential.

Conclusion: Soft starter in most cases; VFD for specialized systems.

....................................................................................

Scenario 4: Offshore Gas Compressor (6 MW, MV)

A fixed-speed compressor operating on a limited power network.
• High power (MW range)
• Strict current limitations
• No variable speed requirement

A medium-voltage soft starter provides controlled current limiting without unnecessary system complexity.

Conclusion: MV soft starter is the correct engineering solution.

....................................................................................

Scenario 5: Data Center Cooling Systems

Modern data centers rely on continuous, stable cooling to maintain uptime.

Case A: Variable Load Cooling
• Cooling demand fluctuates with server load
• Energy efficiency is critical

Conclusion: VFD is the preferred solution.

Case B: Fixed-Speed Infrastructure
• Certain systems operate at fixed speed
• Reliability and simplicity are priorities

Conclusion: Soft starter is a valid solution for auxiliary systems.

The Decision in Practice

Once the application is clearly defined, the selection becomes straightforward:
• Fixed-speed loads → Soft starter
• Variable-speed loads → VFD
• High-power MV systems → Soft starter (in most cases)
• Energy optimization or process control → VFD
• Hybrid environments (e.g., data centers) → Combination of both

A soft starter is not a compromise. It is the correct engineering solution when variable speed is not required.

Need Help Choosing?

Solcon-IGEL's application engineers work with project teams globally to recommend the right motor control technology for every application.

Submit your motor data and application details for a fast, free technology recommendation.

How Does a Soft Starter Work?

Arie.Elkarat@solconigel.com (Arie Elkarat) — Thu, 09 Apr 2026 14:11:11 GMT

The Engineer's Complete Guide

If you've specified motor control equipment, you've encountered soft starters. But how exactly do they work — and why do they work better than the alternatives for a wide range of industrial applications? This guide explains the operating principle, the components involved, and what actually happens inside a soft starter from the moment you press 'start' to the moment the motor reaches full speed.

The Problem with Direct-On-Line Starting

To understand why soft starters exist, start with the problem they solve.

When a three-phase AC induction motor is connected directly to the supply with direct-on-line (DOL) starting, it draws an inrush current of 600–800% of its full-load current (FLA) for the first few seconds of acceleration. On a 90 kW motor with a 160 A FLA, that means 960–1,280 A of inrush current flowing through your cables, switchgear, and transformer for up to 8 seconds. At the same moment, the motor shaft experiences an instantaneous torque application , a mechanical shock through the coupling and into the driven load.

The consequences:

Voltage dips on the busbar that trip other sensitive equipment
Thermal stress on motor windings and starter contacts
Mechanical fatigue on couplings, belts, gearboxes, and pump impellers
Water hammer in pipework when pumps stop suddenly
Utility demand charges triggered by high peak current

The Soft Starter Solution: Thyristor Voltage Control

A soft starter solves these problems using thyristors, specifically silicon-controlled rectifiers (SCRs). A typical three-phase soft starter contains three pairs of SCRs, one pair per phase, connected in anti-parallel (one SCR handles the positive half-cycle, the other the negative). This gives full bidirectional control of each phase voltage.

The key property of an SCR is that it only conducts current during the portion of the AC cycle after it is triggered by a gate pulse. By adjusting the timing of this gate pulse, the 'firing angle' (α) — the soft starter controls how much of each half-cycle is delivered to the motor.

The Starting Sequence — Step by Step

Step 1: Initial Voltage (Pedestal)

At the moment of start, the firing angle is set to a high value (late in the half-cycle), delivering only a small portion of the supply voltage to the motor. This initial voltage is called the 'voltage pedestal' or 'starting voltage' and is typically set between 20–40% of full supply voltage. At this level, the motor begins to develop torque but the current is limited to a user-defined maximum (typically 2–4× FLA rather than 6–8× FLA for DOL).

Step 2: Voltage Ramp

Over the programmed ramp time (typically 5–30 seconds), the firing angle is progressively reduced, meaning the SCRs conduct for a larger and larger portion of each half-cycle. The RMS voltage delivered to the motor rises smoothly from the initial pedestal to full supply voltage. As voltage rises, available torque increases and the motor accelerates the load smoothly, without the mechanical jolt of a DOL or star-delta start.

Step 3: Bypass and Full-Speed Running

When the motor reaches full speed (detected by the current dropping to the running current level), the soft starter activates its bypass. In most modern soft starters, this is an internal bypass contactor that closes to create a direct electrical path around the SCRs, which then stop firing entirely. Some designs use a physical bypass contactor that connects the motor directly across the supply, completely removing the SCRs from the power path.

Either way, the result is the same: the motor runs at full voltage and frequency, with no SCR losses in the steady-state circuit. The soft starter's power consumption during running is negligible.

Step 4: Soft Stop

When the stop command is issued, the soft starter reverses the process. The bypass opens, the SCRs resume control, and the firing angle is progressively increased, reducing the voltage delivered to the motor over the programmed deceleration ramp time. The motor decelerates smoothly, the pump flow reduces gradually, and the check valve closes against near-zero flow — eliminating water hammer entirely.

Current Limiting vs Voltage Ramping

Modern soft starters offer two control modes for starting:

Voltage ramp mode: The voltage is ramped from the initial pedestal to full voltage over the ramp time. Simple and effective for most applications.
Current limiting mode: The firing angle is continuously adjusted to keep the motor current at or below a set limit (e.g., 350% FLA). The voltage rises as fast as the load allows without exceeding the current limit. Better for applications with variable load during starting (e.g., loaded conveyors).

Option 1 – Starting with current limit: Voltage and current rise together until the current reaches the programmed current limit threshold (typically 3–4× FLA). At that point, the voltage holds steady and the SCRs stop advancing the firing angle and remains there until the motor accelerates toward nominal speed and current naturally begins to fall. Only then does the voltage resume its ramp to full supply. This mode gives the tightest control over peak current draw and is the preferred choice for applications where supply capacity is constrained or where other sensitive loads share the busbar.
Option 2 – Starting without current limit: The current-limit parameter is set to a high value so it is never reached during the start. Current ramps up freely as voltage rises, following the natural torque-speed curve of the motor and load. The soft starter still significantly reduces inrush compared to a direct-on-line start, but acceleration is faster and the starting profile is smoother, making this the better choice for light-duty or unloaded starts where speed of acceleration matters more than peak current control.

What the Soft Starter Cannot Do

A soft starter controls voltage, not frequency. Because the output frequency is always equal to the supply frequency (50 Hz or 60 Hz), the motor can only run at its rated synchronous speed and cannot run at reduced speed under normal operating conditions. If your application requires variable speed, you need a variable frequency drive (VFD). For fixed-speed applications, a soft starter is the more cost-effective and reliable solution.

Soft Starter Motor Protection Functions

Beyond starting and stopping, modern soft starters include a comprehensive suite of motor protection functions that eliminate the need for a separate protection relay:

Overcurrent protection and electronic overload relay equivalent
Locked rotor / stall protection (detects motor not accelerating within expected time)
Phase loss, phase reversal, and phase imbalance protection
Thermistor input for direct motor winding temperature measurement
Undercurrent (loss of load) protection — detects pump cavitation or coupling failure
Overvoltage and undervoltage protection
Starts-per-hour limiting to prevent thermal cycling damage

This integration makes the soft starter a complete motor management solution rather than simply a soft start device, eliminating a separate protection relay and simplifying the overall control panel design.

Choosing the Right Soft Starter for Your Application

The fundamental sizing parameter for a soft starter is the motor's full-load current (FLA), not its kW rating. Select a soft starter with a rated current at or above the motor FLA. For heavy-duty applications with long acceleration times (crushers, mills, loaded conveyors), select the next frame size up to provide thermal headroom.

Now let's find your product

If you need more help, we're here

Not sure which model fits your application? Use the selector above to get a recommendation in under a minute. Solcon-IGEL manufactures soft starters from 7.5 kW (LV) to 50 MW (MV), covering every industrial application from standard duty pump control to the most demanding offshore compressor starts. Our application engineers are available to review your motor data and confirm the right product — just use the button bellow.

#Soft Starters

The Long-Term Decision

Izzi Eicher — Sat, 14 Mar 2026 13:55:29 GMT

Why Industrial Soft Starters Are Built for over 20 Years

Ι Some twenty years ago, a plant manager signed off on a soft starter installation. Today, that same unit is still running. He has retired. The machine has not. Ι

When one of our partners made the remark above during a routine strategy meeting, the room went quiet. It sounds like a contradiction, and in most industries, it would be. But in heavy industry, it is simply the truth. And once you sit with it, it changes the way you think about growth entirely.

This Is Not a Short-Cycle Market

Across multiple global installations, Solcon soft starters commissioned more than two decades ago are still operating on the original hardware. Many are only now coming in for their first inspection, minor refurbishment, or a control board review.

That is not an accident. It is the outcome of deliberate engineering choices made at the design stage, choices that compound quietly over time until the evidence becomes undeniable.

Growth in heavy industry is not driven by failure cycles. It is driven by lifecycle decisions. Those are very different conversations — and Solcon is built for both.

Why Solcon Equipment Lasts as Long as It Does

Longevity at this scale does not happen by chance. It reflects a set of conservative, uncompromising engineering principles applied consistently across every unit:

Stable thermal management — The unit never runs hotter than it has to. Most electronics die quietly from heat long before any visible failure.
Conservative component ratings — Every component is designed with a safety margin to withstand unexpected stress in the application — not simply rated to the minimum requirement.
Durable control architecture — Designed to be maintained and updated, not discarded when modernization is needed.
Industrial-grade electronics — Built for the real conditions of a plant floor — heavy duty design for vibration, dust, humidity, and continuous duty.
Mechanical design and testing — The mechanical design accounts for the operating environment and is validated under severe test conditions — ensuring durability before a unit ever reaches site.

The result is a unit that ages gracefully. Not one that simply survives — one that continues performing as intended, decade after decade.

Built on Five Engineering Principles

Every design decision serves a single goal:

equipment that performs decades from now, not just today.

🌡

Thermal Stability

Runs cool under load. Heat is the primary cause of silent electronics failure.

⚙

Conservative Ratings

Components rated beyond application stress — not matched to minimum requirements.

🏗

Durable Architecture

Designed to be maintained and modernized, not replaced at the first sign of age.

🔌

Industrial Electronics

Built for real plant conditions: vibration, dust, humidity, and continuous duty.

🔧

Mechanical Durability

Designed for the operating environment and validated under severe test conditions before reaching site.

If You Have a Solcon Unit Running Right Now, Read This

If a Solcon soft starter has been running in your facility for a decade or more, you are not sitting on aging equipment.

You are sitting on a proven asset.

The question is no longer “when will this fail?” That framing belongs to a different kind of product. The relevant question for your operation is: how should this asset evolve?

Facilities with long-serving Solcon units are now making decisions like these:

Refurbish the unit to extend operational life by another decade — and introduce new features in the process
Modernize the control electronics while keeping the robust power section intact
Update protection functions to align with current safety and compliance standards
Integrate communication protocols for smarter plant management systems
Upgrade performance or connectivity capabilities ahead of plant expansion

These are not replacement conversations. They are evolution conversations — and they represent a fundamentally different kind of partnership between manufacturer and customer.

Your Installation Is a Strategic Asset

An installation that remains operational after 20 years is not a limitation on future revenue. It is a foundation for a deeper relationship.

Every long-serving Solcon unit in the field represents:

A relationship built on demonstrated reliability — not promises
A proven application reference in your specific operating conditions
A modernization opportunity that avoids the disruption of full replacement
A digital upgrade pathway — remote monitoring, diagnostics, protocol integration
A service engagement point built on trust earned over years

This is why the most forward-thinking industrial facilities are not asking us for new units to replace their old ones. They are asking us how to get the most out of what they already have — while making it ready for the next generation of operational demands.

Modernization Without Disruption

Major plant shutdowns are expensive and disruptive. Most facilities will do almost anything to avoid them — and with a Solcon unit, they often can.

Where the power section remains structurally sound, modernization can be targeted and surgical. That might mean updating a control board, enhancing protection functions, integrating a fieldbus communication protocol, or improving monitoring and diagnostics to give your team real-time visibility into motor performance.

Plants get measurably better performance and far greater operational visibility — without a full system redesign or an extended shutdown window. That matters enormously to any facility manager responsible for uptime.

The Sustainability Argument Is Real

Long service life is not just a financial argument — it is an environmental one. Extending the lifecycle of industrial equipment reduces material waste, minimizes disposal impact, and preserves the significant energy already embedded in manufacturing the original unit.

At a time when industrial ESG commitments are under increasing scrutiny, choosing to extend rather than replace is a decision that holds up in every boardroom conversation — financial, operational, and environmental.

Total cost of ownership across a 20-year horizon looks very different from a 5-year horizon. Solcon customers who run the full calculation understand this intuitively.

The Lifecycle of a Solcon Installation

A typical asset journey — from commissioning to decades of productive service.

Year 0

Commissioning

Installation, configuration, and handover to plant team.

Year 5

Proven Reliability

Unit performing within original parameters. First service review.

Year 10

Lifecycle Assessment

Strategic review. Retrofit or monitoring upgrade options evaluated.

Year 15

Modernization

Control board or protocol upgrades. Remote diagnostics integrated.

Year 20+

Still Running

Operational. Refurbishment or next-generation upgrade planned.

If Quality Is “Too Good,” Build Around It

Our partner’s remark was made as an observation about market dynamics. We took it as a design brief.

In heavy industry, reliability is not a marketing claim. It is demonstrated across decades of operation, under real industrial conditions, in facilities around the world. When soft starters remain in operation 20 years after commissioning, that is not a coincidence — it is engineering integrity made visible.

The strategic question for Solcon has never been whether to lower quality to drive replacement cycles. The answer to that question is no. It has always been no.

The question we ask instead is: how do we build a growth strategy worthy of equipment this good?

The answer is lifecycle partnership. Service. Modernization. Retrofit programs. Control upgrades. Remote diagnostics. And a relationship with our customers that outlasts any individual piece of hardware.

The best time to plan the next 20 years is before you need to.

That conversation starts with us.

How Semiconductor Fabs Cut Compressor Downtime with Withdrawable Medium Voltage Soft Starters

contact@solconigel.com (Solcon-IGEL Marketing Team) — Mon, 09 Feb 2026 13:44:02 GMT

When Downtime Is Not an Option

In semiconductor manufacturing, minutes matter. Utility systems such as compressors, chillers, HVAC run continuously to maintain the precise conditions that production tools demand. When one of these systems goes offline, the impact doesn't stay local. It ripples through the fab.

The question most facility engineers never get to ask is: when we do need to service or replace this equipment, how fast can we get back up?

For one of our customers, a semiconductor manufacturer running compressors on medium voltage. That question drove a decision that changed how they think about their entire electrical infrastructure.

The Challenge:

Servicing a compressor that can't easily stop

Compressors in semiconductor fabs supply clean, dry compressed air to pneumatic controls, automation systems, and process support equipment. In most fabs, a single compressor system serves multiple tools across multiple production areas. That interdependency is its own kind of fragility.

When the time came to service or replace the starter, the traditional approach, a fixed-mounted starter, created a serious operational problem. Replacement meant:

Extended shutdown windows - dismantling panels and disconnecting power connections that weren't designed to be undone quickly
Complex isolation procedures - coordinating between electrical, mechanical, and process teams before anything could be touched
Extended recovery time - every additional hour offline directly impacted production yield

The starter itself wasn't the most expensive component in the system. The downtime to replace it was.

The solution:

Withdrawable Medium Voltage Soft Starter

To address this, the facility installed a withdrawable medium voltage soft starter, specifically, an 11kV, 140A system built around Solcon's HRVS-DN platform , in a metal clad enclosure with a complete IP00 chassis draw-out design.

The key feature is mechanical simplicity under pressure. The HRVS-DN chassis can be physically withdrawn from the enclosure without dismantling the surrounding panel or disconnecting the main power connections. In a maintenance event, the unit slides out. The replacement slides in. The panel stays intact.

What this looks like in practice

Maintenance teams no longer need to coordinate a full panel shutdown to service the starter. A trained technician can withdraw the chassis, perform the work or swap in a replacement unit, and restore operation, without the multi-team shutdown event that traditional fixed starters require.

For a compressor serving multiple production areas, that difference in recovery time is not marginal. It's the difference between a controlled maintenance window and an unplanned production impact.

Key technical features

IP00 draw-out chassis - Enables full withdrawal and replacement of the soft starter without disturbing the enclosure, panel, or power connections
11kV rating (2.3–13.8kV operating range) - Sized for large compressor motors at medium voltage, with controlled ramp-up to limit inrush current and mechanical stress
Metal clad enclosure - Provides fault containment and personnel protection in line with IEC standards - essential for fab environments
Enhanced motor protection package - Integrated overload, phase-loss, thermal, and current unbalance protection reduces unplanned failure risk between planned maintenance intervals

For full specifications, see the HRVS-DN product page.

What this means

For semiconductor operations

The value of a withdrawable design isn't visible during normal operation. It shows up when something needs to change, whether that's a planned maintenance cycle, an unexpected component failure, or a future upgrade.

For fabs managing uptime as a core production metric, maintenance procedures that are predictable, fast, and contained represent a measurable operational advantage. They reduce the exposure window, lower the coordination burden, and keep the facility's electrical infrastructure from becoming the variable that limits production availability.

In semiconductor manufacturing, the true value of electrical equipment is measured by how quickly operations can recover from maintenance or failure events , and not just how reliably it runs on a normal day.

The bottom line

A withdrawable medium voltage soft starter doesn't change what the equipment does. It changes what happens when the equipment needs attention.

For semiconductor fabs, where compressors run continuously, where downtime cascades, and where every maintenance event carries operational risk - that distinction is worth thinking carefully about at the specification stage, long before the first service call arrives.

#Medium Voltage Soft Starter

Solcon - IGEL

Soft Starter vs VFD

Which Is Right for Your Application?

ears

The One-Sentence Rule

Scenario 1: Municipal Water Supply Pump

Scenario 2: HVAC Air Handling Unit (Variable Demand)

Scenario 3: Mining Conveyor (Loaded Start)

Scenario 4: Offshore Gas Compressor (6 MW, MV)

Scenario 5: Data Center Cooling Systems

The Decision in Practice

Need Help Choosing?

How Does a Soft Starter Work?

The Engineer's Complete Guide

The Problem with Direct-On-Line Starting

The Soft Starter Solution: Thyristor Voltage Control

The Starting Sequence — Step by Step

Current Limiting vs Voltage Ramping

What the Soft Starter Cannot Do

Soft Starter Motor Protection Functions

Choosing the Right Soft Starter for Your Application

Now let's find your product

If you need more help, we're here

The Long-Term Decision

Why Industrial Soft Starters Are Built for over 20 Years

This Is Not a Short-Cycle Market

Why Solcon Equipment Lasts as Long as It Does

If You Have a Solcon Unit Running Right Now, Read This

Your Installation Is a Strategic Asset

Modernization Without Disruption

The Sustainability Argument Is Real

If Quality Is “Too Good,” Build Around It

How Semiconductor Fabs Cut Compressor Downtime with Withdrawable Medium Voltage Soft Starters

The Challenge:

Servicing a compressor that can't easily stop

The solution:

Withdrawable Medium Voltage Soft Starter

What this looks like in practice

Key technical features

What this means

For semiconductor operations

Related solutions

The bottom line