The Low-Voltage Observability Problem

Learning objectives

By the end of this lesson you should be able to:

Understand what is meant by observability in power systems.
Explain why observability is essential for operating electricity networks.
Recognise the differences between transmission and distribution network monitoring.
Appreciate why low-voltage networks have historically had limited visibility.
Understand how increasing numbers of distributed energy resources are exposing this limitation.
Recognise why improved observability is a prerequisite for smart grids.

Introduction

Imagine trying to drive a car without being able to see through the windscreen.

You might know where the road begins.

You might know where it ends.

But you would have very little idea what was happening in between.

Operating an electricity network presents a similar challenge.

Before operators can control a system, they must first observe it.

This principle is fundamental to every engineering discipline.

You cannot effectively manage what you cannot measure.

As electricity systems become increasingly distributed, the ability to observe what is happening throughout the network is becoming one of the most important challenges facing modern power systems.

What is observability?

Observability refers to the ability to determine the operating state of a system using available measurements.

For an electricity network, this means understanding quantities such as:

voltage,
current,
power flows,
transformer loading,
equipment status,
network topology.

If operators cannot estimate these quantities with sufficient accuracy, they cannot confidently determine how the network is behaving.

Why observability matters

Every operational decision depends upon knowing the current state of the network.

For example:

Can another electric vehicle begin charging?

Can a battery export electricity?

Is a transformer becoming overloaded?

Is voltage approaching its allowable limits?

Without sufficient measurements, these questions become difficult to answer with confidence.

Observability therefore underpins safe and efficient network operation.

Transmission networks are well monitored

The high-voltage transmission system is generally equipped with extensive monitoring equipment.

Operators receive measurements from:

substations,
transmission lines,
transformers,
protection equipment,
phasor measurement units (PMUs),
supervisory control and data acquisition (SCADA) systems.

These measurements allow transmission operators to estimate the state of the network with a high degree of confidence.

The transmission system is therefore highly observable.

Distribution networks are different

Historically, distribution networks were designed very differently.

Their primary purpose was simply to deliver electricity from substations to consumers.

Power flowed in one direction.

Demand was relatively predictable.

Few operational decisions needed to be made within individual streets or neighbourhoods.

As a result, relatively little monitoring equipment was installed.

Many low-voltage feeders contain very few real-time measurements.

In some cases, operators know:

how much power enters a distribution transformer,

but have very limited visibility of what happens beyond it.

Why wasn't more monitoring installed?

Historically, there was little need.

Most households simply consumed electricity.

Individual customer demand was relatively small.

Power flowed predictably from substations towards consumers.

Installing sensors throughout every residential street would have provided relatively little additional benefit while significantly increasing costs.

The network was therefore designed to operate safely using conservative engineering assumptions rather than continuous real-time observation.

The system has changed

Today's electricity networks are very different.

Many homes now contain:

rooftop solar,
batteries,
electric vehicles,
heat pumps,
smart appliances.

Instead of simply consuming electricity, customers increasingly influence how the network operates.

Power flows change more rapidly.

Voltage becomes more dynamic.

Local congestion becomes more common.

Yet much of the underlying monitoring infrastructure remains unchanged.

The observability gap

This creates what is often called the low-voltage observability problem.

The physical system has become increasingly dynamic.

However, operators often have only limited visibility of these changing conditions.

In other words:

The complexity of the network has increased much faster than its ability to observe itself.

State estimation

Because direct measurements are often unavailable, network operators frequently rely on state estimation.

State estimation combines:

available measurements,
network models,
engineering knowledge,
statistical techniques,

to estimate quantities that cannot be measured directly.

For example, if measurements exist at only a few locations, mathematical models may estimate the voltages and power flows elsewhere in the network.

State estimation is therefore a powerful tool—but it is still an estimate.

Its accuracy depends on both the quality of the models and the quality of the available measurements.

Why uncertainty matters

Limited observability introduces uncertainty into operational decisions.

Consider a neighbourhood containing hundreds of electric vehicles.

If operators cannot accurately determine:

current loading,
local voltage,
available network capacity,

they must often adopt conservative operating practices.

This may mean restricting the use of network capacity even when additional capacity is actually available.

Limited information can therefore reduce the efficient utilisation of existing infrastructure.

More sensors, more information

One solution is to improve observability.

Modern electricity systems increasingly deploy:

smart meters,
feeder monitors,
transformer sensors,
voltage sensors,
intelligent electronic devices,
advanced communications.

Together, these technologies provide a much richer picture of how distribution networks are operating.

Better information allows better decisions.

Observability enables smart grids

Smart grids are often associated with automation, artificial intelligence or advanced markets.

However, none of these technologies can operate effectively without sufficient information.

Observability is therefore one of the fundamental building blocks of a smart grid.

A system cannot intelligently coordinate distributed resources if it cannot observe what those resources are doing.

Measurement comes before optimisation.

Observation comes before control.

Data becomes part of the electricity system

Historically, electricity systems transported energy.

Increasingly, they also transport information.

Measurements collected throughout the network become essential operational resources.

Electricity networks are therefore evolving into cyber-physical systems in which:

physical infrastructure transports electrical energy,
digital infrastructure transports information.

Both are necessary for reliable operation.

Opportunities

Improved observability offers many benefits.

These include:

greater utilisation of existing networks,
improved operational safety,
better voltage management,
faster fault detection,
increased renewable integration,
more accurate operational decisions,
greater use of distributed flexibility.

Information becomes a valuable engineering resource.

Challenges

Improving observability also presents challenges.

These include:

installing large numbers of sensors,
communications infrastructure,
cybersecurity,
managing vast quantities of data,
ensuring interoperability between devices,
maintaining data quality.

Building a fully observable electricity network therefore requires both physical and digital investment.

A key insight

Modern electricity systems are becoming increasingly distributed and dynamic, yet much of the low-voltage network remains only partially observable.

Without sufficient visibility, operators must often rely on estimates and conservative assumptions when making operational decisions.

Improving observability is therefore one of the key enabling technologies for the future smart grid, providing the information needed to safely coordinate millions of distributed energy resources.

Key takeaways

Observability describes the ability to determine the operating state of an electricity network.
Transmission networks are generally well monitored, while low-voltage distribution networks often have much more limited visibility.
Distributed energy resources have made low-voltage network operation significantly more dynamic.
State estimation is used to infer network conditions where direct measurements are unavailable.
Limited observability can reduce the efficient utilisation of existing network capacity.
Improved sensing and communications enable better operational decisions.
Observability is a fundamental prerequisite for smart grids and advanced network coordination.

Looking ahead

Improving observability is only one part of the transformation occurring within electricity systems.

Measurements alone do not operate the grid—they must be combined with communications, automation, software and control.

In the next lesson, we examine digital infrastructure and smart grids, exploring how these technologies are enabling a new generation of electricity system operation.