<t t-set="productname" t-value="line.name"/>
<t t-if="len(productname) > 30">
<t t-foreach="range(0, len(productname)+1, 30)" t-as="product">
<span t-esc="productname[product:product+30]"/><br></br>
</t>
</t>
<t t-else="">
<span t-esc="productname"/>
</t>

Thanks it works, but how can I avoid splitting the words? I mean to make the new line before the word starts

To avoid word splitting it's a little difficult, for that you can call python function and build logic from there.