Why Choose a kW-Based Load Monitor? What Engineers Need to Know About Unipower HPL110 and HPL500
Are current or power factor monitors really protecting your motor?
If you've ever Googled...
"Why does my motor protection relay keep false tripping?"
"Can I monitor load after a VFD/inverter?"
"Best way to detect dry-run or overload on a pump?"
...you’re not alone. These are some of the most common questions engineers and panel builders type into search engines every day.
And here’s the simple truth: most traditional load monitoring methods are outdated. If you're relying on current monitoring or cosφ (power factor) protection, you're probably not getting the full picture — and it's likely costing you reliability, time, and money.
The Problem with Current and Cosφ Monitoring
Let’s break it down:
Current is not proportional to motor load — especially under partial load conditions.
Cosφ (power factor) varies with load and motor design, making it inconsistent.
Both methods are affected by supply voltage fluctuations, leading to false alarms or missed faults.
So how do you accurately and consistently monitor load?
Why kW (Real Power) Monitoring is the Smart Alternative
Unlike current or cosφ, kW is directly proportional to mechanical load. That’s the beauty of measuring true active power (P) using the formula:
P = √3 × U × I × cosφ
Here’s why that matters:
kW gives a linear response to load changes
It's immune to voltage variation
It works even on distorted waveforms, such as those coming after a variable frequency drive (VFD)
That’s exactly where the Unipower HPL110 and HPL500 shine.
What Makes the Unipower HPL110 a Game-Changer?
The Unipower HPL110 is a compact, DIN-mounted load monitor for 3-phase AC motors. It directly calculates kW, giving you the most accurate load condition feedback possible.
Key benefits:
Built-in current transformer up to 8A
External CT support for larger motors
Simple parameter setup
Adjustable Min/Max limits and reaction timers
Auto-reset with hysteresis to avoid nuisance trips
It’s the ideal choice for:
Pumps and blowers (detect dry-run or overload)
Mixers and conveyors
Fans, grinders, and process motors
Why HPL500 is Perfect After an Inverter (Where Others Fail)
You might be thinking:
“But I use a VFD — can I still monitor motor load accurately?”
Most devices like the Emotron M20 cannot handle post-inverter loads due to distorted waveforms.
But the Unipower HPL500 can.
It uses a fast 4-quadrant multiplication method to accurately measure real power — even on inverter outputs.
Why HPL500 stands out:
Works from 100–575V, single or 3-phase
Internal current range up to 40A (external CT up to 600A)
Dual relay outputs + analogue (4–20mA)
Optional shaft power (P2) calculation with motor efficiency modelling
MODBUS RTU and PC configurability (HPL500-MB & HPL500H)
Still Not Sure? Ask Yourself This:
If you're designing or upgrading a motor control system and wondering…
✅ How do I get reliable load detection after a VFD?
✅ How do I avoid tripping from fluctuating supply voltages?
✅ What’s the best way to protect pumps from dry-running or cavitation?
✅ Can I get a simple analogue load signal into my PLC or BMS?
Then you need to monitor real kW — and Unipower is the answer.
Get Started With Unipower
We stock and support the full range of Unipower products, including:
HPL110 — for compact motor monitoring
HPL500 — advanced monitoring after VFDs
HPL530, HPL540, HPL503 — for shock loads, kWh, conveyor reversal and more
🛒 Browse the full range here
📩 Contact us for help specifying the right product for your panel.
Bonus Downloads
📄 HPL110 Datasheet (PDF)
📄 HPL500 Overview (PDF)
Conclusion
If you're still using current or cosφ-based protection, you're missing out on precision, reliability, and peace of mind.
Unipower load monitors give you the clarity, flexibility, and integration options modern motor systems demand.
“Buyers today want to be educated. Not sold to.”
— Marcus Sheridan, TAYA
This post isn’t just to tell you why Unipower is better — it’s here to help you understand what works in the real world. And that’s what we’re all about.